Hear, Hear.
I always pin my number, unfolded, on the middle of my vest.
If I have to put a jacket over the top, I always unzip it (no matter how foul the weather) so that the marshals can see it
I never shout out my number, as I might mis-remember it, the marshals might mis-hear, plus the marshals have no way of being sure that I am not somebody without a number just "blagging it"
I do all of the above not because it is in the FRA Safety Requirements Document, not because the Race Organiser has required it and not because I am some sort of goody two shoes, but FOR MY OWN SAFETY.