∨ is the mathematical symbol for "or" (in logic) -- my guess is that it may be derived from the fact that the initial letter of the Latin word for "or" is "v". There's a kinda convention that when you have a(n associative) binary operator, you use a bigger version of it to signify applying it to all the things in a sequence or set, so you'd want a larger one -- a bit like a capital "V".

⊤ is the mathematical symbol for the "top" element of a Boolean algebra; maybe more generally of a lattice. You wouldn't use it to mean "maximum of these things" in general.