I have advertised birthday specials for three years (discounted sessions all month)....most gentlemen interested, start their email...
"My birthday is this week and I would love to celebrate it with you. Are you available?"
Whether they have seen my ad or not, I know to respond, letting them know of my special etc. Although I wouldn't mind if a gentlemen said, " I want to take advantage of your offer", the above approach may help the ones less comfortable.