While we are only required to use #38 (personal foul) prior to #45 (face mask) and #30 (roughing/running into kicker/holder) to indicate a 5 or 15 yarder, I usually precede the following signals with #38 : #24,25,39,40,41 & 46. IMHO, this clarifies that a 15 yarder is coming and most everyone knows the PF signal. Over the years I've had #41 mistaken for #18(encroachment), #24 mistaken for #23 (failure to wear required equipment) and #46 mistaken for #30 (running into the kicker). This helps the PA announcer to get it correct or at least announce : "PERSONAL FOUL".