They play a lot of hands... a lot
If they're playing two or three hands an orbit they're probably not playing just big pairs.

'It's my turn... I raise'
If the action is passed to them pre-flop they very often open the betting with a raise.

They're a good LAG
When the big bets go in and the cards are turned over they always have the goods.

They wear a LAG t-shirt
These have catchy slogans on them like, 'I'm LAGging ahead of the pack.' They're working on the slogans...