ACR is one of my staple card routines, I do it every show/performance/street walk-around. Probably already been said to death; but a little showmanship, talking and humor goes a long long way with any routine, especially an ACR. Try to make a story about the signed card, or just act surprise as the routine takes place, or do it in complete silence, using only body language to sell the routine. As long as the spectator has an open mouth in surprise, or says the classic line, "How did you do that??" then you've succeeded regardless of how it was performed.
ACR for life!