I believe this is the 'Term' for what you are referring to;
To call with one motion and raise with another, or to reach for more chips in the middle of laying a bet/raise without stating the intended amount. String bets are prohibited in public cardroom rules
. <--Wiki pedia
Unannounced Bet is binding once the chips cross the line towards the pot.
ie. 500 single chip bet, first to act where Big Blind is less than half of 500 (say, 200BB/100SB)
and this would be considered a 'Raise' - unannounced when put across the line.
All Verbal announcement is binding.
'Call' = match original Bet (or Raise).
'Raise' = Minimum of Double the original Bet
'Re-Raise' = Minimum of Double the original Raise
Glossary of poker terms - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Glossary_of_poker_terms#S)
Another is to say 'I raise' and put 'x' amount into the pot, and then reach for more to put in.
The motion has to be in a 'Single' Motion, and no additional Chips may be added to the Pot.
String Bet also include Calling, or Raising out of Turn,
where you will get a warning from the dealer or Director,
and get a 1 level penalty,15 min. Sit-Out.
(All Blinds and Antes are forefeited the next time it happens.)