There are three types of signals:
Attitude signals
This means simply telling your Partner whether you like the lead or not,
and of course this will also apply as the play progresses.
Usually a high card is encouraging and a low card is discouraging. But some play what is known as reverse attitude and the opposite applies
Count signals
This is only used when following suit and when an attitude signal isnt relevant,
The usual method is to play a small card from an odd number and a high card from even.
If Partner starts with Ace ( from Ace King) of a suit they have bid a count signal may be vital.
It is usually easy for the leader to differentiate between them.
When Declarer leads a count signal is normal, which should help Partner to count Declarers hand.
When trumps are lead it is modern practice to play reverse count signals which can help Partner to decide whether you have a trump left to gain a ruff.
As long as you are agreed which you are using I don’t think it makes much difference.
Suit-preference signals
These tell Partner which suit to switch to.
It is not always easy to read but
practiced Partnerships can usually realise which from their holding and Dummy.
The easy one is when Partner leads an Ace and Dummy goes down with a singleton, (against a suit contract)
the card you play should always be a suit preference signal
Another situation is when you have lead a card to give Partner a ruff.
If possible the card you lead should indicate which suit Partner should lead back possibly to allow a second ruff or just to ensure a trick is
cashed in time
For example you hold ♠ A964 ♥ 94 ♦ 75 ♣ A9652 Partner leads a Club.
You take the Ace and lead the ♣9 back for a ruff- the 9 asking for the highest suit back, Spades
When not to Signal.
When you hold most of the remaining points and knowing Partner will never gain the lead, don’t Signal, it will only help Declarer. Play false cards to try and confuse them.
Conversely if you have absolutely nothing left and you know or suspect your Partner has,then the reverse applies and you should signal accurately to try to help Partner. Against a slam unless Partner leads an Honour don’t signal as again it is more likely to help Declarer