Dear Ed & Peter,

Can you tell me if the following discard system has a name please: Any 234 asks for the lowest of the three remaining suits to be led 567 asks for the middle suit to be led 8910 asks for the highest to be led.
My partner introduced me to this system but she has no idea what it is called - I find it much easier than McKinney

Thanks,
Wendy

Reply from Ed Hoogenkamp ('South'):

Dear Wendy,

I'm not familiar with this discard system. I've looked around on the internet, but could not find a name. One observation though: there is a reason this system is not well known. At first glance it seems to work perfectly....if you have the right cards to play. Often you don't. Then the system starts to fail and in some cases the famous 'slow signal' appears. I want to warn everybody to handle these situations (you want to give a certain kind of signal but lack a suited card) with extreme care: a slow signal is very human but also very illegal!

A signal system like this is very vulnerable to mix-ups because the meaning of every card is exact.
In standard signalling, like high is encouraging, this is not the case because at the table you can interpret whether a card is high or low (a four can be high and an eight can be low, depending the circumstances). Misinterpretation in standard signalling is possible, but rare.
In your system, which has an exact meaning for every card played, partner in some cases has no choice but to misread your card. In other words: he will go wrong with 100% certainty (hence the earlier mentioned slow signal, you are provoked by your inability to give a proper signal...)

This doesn't mean of course you shouldn't play this system. Everybody should play the system that's best for him or her.
I'm sorry I couldn't help you, maybe Peter can (he knows a lot!!) (Crawler, -Peter)

(If he doesn't I hereby call upon readers to react if they know the name of this discard system).

Regards from Barcelona

Reply from Peter van der Linden ('North')

Dear Wendy,

I think the system you mention is not a known one, probably it is 'locally famous'.
Like Ed I think it is too rigid. If you want to signal for the highest of three suits you must throw an eight, nine or ten. But what, like Ed says, if you don't have one, or, more frequently, you can't spare one...?
A more profound, even fatal weakness of the system is that it caters for signals in all three suits. This means every discard is a signal. This leads to even more rigidness and is highly impractical because (very) often a player simply can't overview the hand and cannot therefore decide what signal to give. Or he knows that his partner should decide about the switch, since he (partner) has the information. If every card you play is a signal partner might be tempted to follow your signal (based on nothing really) instead of following the path his own hand suggests.
Therefore you need to be able to signal 'neutrally'.

Although not an expert in this field, I will try to talk you out of your system (sorry...) and give some information about better ones.

McKenney, better known as Lavinthal on our side of the ocean (bridgevaria.com is originally a Dutch site) and Revolving Discards resemble 'your' system a bit but are definitely better because they allow a 'neutral' signal. Both exclude the suit of the discard, leaving two suits to signal for.
- McKenney/Lavintal. Suppose you throw a heart on a spade trick. This means you don't want partner to play hearts. A high heart asks for the higher of the other two suits (diamonds) a low heart therefore asks for a club.
A middle heart would be a neutral signal then.
You might also signal diamonds by way of a low club, signal hearts by way of a high diamond or club and so on.
But this too is cumbersome, often you just cannot afford to discard a card you 'have to' discard according to the system.
- Revolving discards: here you operate with 'ranking' suits: a high club asks for a diamond, a low club for a spade, a high diamond for a heart, a low diamond for a club, a high heart for a spade and... well, you get the picture I guess.
The neutral signals are the ones that ask for the suit in which you are showing out (confusing yes, I mean: by discarding a high heart or a low club in a spade trick you would ask for a spade, a suit in which you are showing out, right?).

Something to chew on: few experts use the signals in the way (as discards) discussed above. Again because these signals are too rigid.
Revolving discards is slowly becoming obscure.
Lavinthal (McKenney) is very much in use but not in discarding! Experts use it sometimes when following suit in trumps: playing trumps high-low would then ask for 'the' higher suit. 'The' higher suit? Aren't there three suits left? Yes, but this is less vague than it looks like: usually one of the three suits is clearly not an option, leaving two. Playing trumps low-high would be neutral, not per se asking for the lower suit!
(But please note: a signal in the trump suit by the partner of the opening leader can also be a Smith signal, showing whether or not he liked that opening lead).
Lavinthal is also used when giving partner a ruff: a high card asks for a return in the higher ranking (of two!) suits.

So discarding systems in which the height of the discard contains a message about the suit to play back are not popular among experts because they are too rigid and make bridge players 'follow orders' rather than think.

There is one exception: Roman signals, sometimes called Italian signals. These are not only used in discarding, but also when following suit in a trick begun by partner. The idea is:
1. An odd card is encouraging, an even card is discouraging.
2. An even card can (!) also convey a 'Lavinthal (McKenney) message':
    - A high even card asks for the higher of 'the' other two suits (in a trump contract this is obvious since the trump suit is not an option; in a no trump contract usually one suit is obviously not an option).
    -A low even card can (!) ask for the lower of the other two suits, but only if the signaller is known to have a choice of cards to play (a long suit therefore). If he has not, the low even card is discouraging only and has no Lavinthal meaning.
    - A middle high even card is the neutral card if the player is known to have a choice.
Note that this system is not easy; it is not a toy for inexperienced players.

To conclude I give you my advice: keep it simple!
- Play encouraging and discouraging signals 'in the suit' when discarding or following suit in tricks partner begins.
When discarding a discouraging signal is often good enough for partner, he can usually see that one of the other two suits is out of the question. That leaves one suit only.
- In very clearly defined cases a high or low card can have a Lavinthal meaning.
- Show your distribution in suits declarer plays if you think it is important for partner to know. If the distribution clearly is unimportant you can in exceptional cases give a Lavinthal signal then, for instance when declarer draws trumps. 

Further reading:
http://www.pattayabridge.com/conventions/Signalsindefence_main.htm
http://www.gwilliams.org.uk/signals/index.html
...and of course Wikipedia:
http://en.wikipedia.org/wiki/Signal_%28bridge%29

Regards from Orkanger