[math-fun] Sign conventions

What's the canonical example of two scientific communities that have adopted mutually inconsistent sign-conventions? (Do physicists and electrical engineers describe electric fields using different sign conventions, maybe?) This relates to my most recent "bizarro arithmetic" post inasmuch as Martinez seems to be inviting us to imagine that normal and bizarro arithmetic could be set up as separate self-consistent systems, with a dictionary that lets you convert true statements in one system into true statements in the other. I'll believe it when I see it... Jim Propp