I believe at my level I do not use the same mechanics manual you are referring to, but it's interesting to know that the higher levels are directed to use the signal, thanks.
My opinion is based on the NCAA Rule Book, page FR-113. For example on Face Mask it shows S38 and S45, for Horse Collar it shows S38 and S25, and for Roughing the Kicker is shows S38 and S30. However, for Roughing the Passer only S34 is listed.