A carom player taps his chalk on the side of his cue to complement a nice shot. If the audience is applauding, the player will wait until the applause has died down so his opponent can hear.
A snooker player coming to the table after his opponent has played a good safety will tap/place their cue gently on the rail or pat the table.
Like here https://youtu.be/2LtnKJDfQyk?t=1m47s
There was one that is actually a recent post where the opponent was clapping on the table.