When something like this happens I put my right arm straight out pointing at the play. This starts the mechanic of making the call. I then take a half second to full second to make sure I got the call right. At this point I either make a fist & make the out call & signal or I'll extend my left arm straight out next to my right arm and make the safe call. Doing this lets everyone involved know you're making the call. This mechanic has yet to fail me & I've never had confusion on what I call.
I probably shouldn't say this but I learned this several years ago from one of my assigners who is a D1 ump and now working as a fill in doing AAA ball.