AlexL
Contributor
For an S-drill, the common signal is an "S", followed by what you want to do
doesn't really matter as long as you and your buddy / team is/are on the same page, but for what its worth with some agencies the S sign/S-drill is explicitly for the reg donation drill.
in our buddy pair, as soon as you sign 'S', the other party immediately signs 'OK', 'OOA', readies their backup / bail out, and spits out their primary reg. can get a bit confusing with a 3rd party instructing the start of a S-drill, so during our fundies class the team agreed pre-dive to a modification to the signing as you had mentioned; sign S, then point to the person doing the donation, and then who is to receive. this is then echoed by 'OK', 'S', and pantomime 'as you wish' (hands to chest, then roll forward to palms up) to the receiver, with a final 'OK' to receiver which is echoed back to the donor, and the drill begins.