robint, many newer divrrs haven't seen an arrow crab or even ever looked at one closely enough to notice its beautiful blue claws. I like to show fellow divers small things through my magnifying glass.
If other divers have had arrow crabs pointed out to them before they still may not yet have made the link with the corkscrew anemone. Just the other day, I saw a corkscrew anemone right out full in the sand and of course a lovely arrow crab sitting peacefully right in the middle, just as I turned, the anemone slipped itself halfway back under a small rocky outcrop, just the way I more commonly spy them. I was delighted and so was the dm.
Perhaps you are hohum over such minor events but I'm not and neither is everyone else. How are we to know once underwater that you aren't interested?
And Greg, I generally don't care to have another Caribbean lobster pointed out to me but I don't know what the pointer may spy next. Ergo I'll still be taking a little interest in what's pointed out to me, unless it's lobster, lobster, lobster.
I shan't ever tire of seeing juvenile drums dance.
OK back to signaling. I do my best but many vacation divers don't know all signals. As others have said before me, I also try to show that it's wee or grande and under a ledge. I'm also often completely inverted with finger pointing and within mere inches of the wee subject.