[mcrowder]

The only "secret" signal I can think of that I use with partners I'm VERY familiar with is more the reverse of what you're talking about. As PU, I'm not making any sort of signal to BU (or to the world) to alert him (and the world) that I think he botched a call - and vice versa as the BU.

However, having worked with 3 or 4 guys on many occasions, if the BU is calling a plate at 1st base, for example, and HE (not I) thinks there is a possibility for a pulled foot that he missed because of an unanticipated straight-line, during his normal hesitation between the play and the call, he'll glance at me (PU). If I am 100% sure I saw a foot pulled, I'll quickly lift my foot (looks like a small, quick step in place), and HE'll make the safe call, and then point at the foot saying "Pulled his foot", or something along those lines. With no footpull (or at least not 100%), I stand still, and he makes the normal out call, then also knowing that if the coach asks him to check with me, he can tell the coach he already did, and the call stands.

But this is really just shorthand for us and looks cleaner than calling him out, and then asking more obviously (to the world) if PU saw a foot pull.

I know there are a few here that NEVER ask partner for help. I see the straightlined footpull and the straightlined swipe tag as two clear instances that even the BEST umpire knows he may have missed once every year or two.