With four deuces, you agree to "psych" 1♠. With four threes. you agree to "psych" 1♥. And so on. You can use as many specific combinations of small cards as you can remember. For example with ♣2 ♦3 ♥4 and ♠5 you can agree to "psych" 1N.
Thus, in any specific context, each psychic call has a unique trigger.
If partner is suspicious of any call, he can sometimes reassure himself by looking at his own hand. For example if your 1♠ opener seems fishy to partner, he will be reassured if his hand contains any deuce. If his hand is deuceless, however, then he may well be more wary.
Among the advantages of this approach are:
- Psychs are rare (because these card-combinations are rare).
- You "psych" pseudo-randomly (because of the random nature of deals)
- It's hard for observers to detect (unless they know its rationale).
- Partner has a good chance of fielding your psych (from inspecting his own hand).
- It's hard for opponents to combat (even if it were legalized and you declared it).
If this kind of thing were legal, however, the game might be more exciting.