Symbol for 'Or'
Vel, "∨", is the symbol for logical disjunction, "or", in symbolic logic. The Wikipedia entry notes that Russel and Whitehead used the symbol in their Principia Mathematica of 1910. As several commenters have noted, various systems of formal logic employ alternative symbols, including "+" and "∥", to represent this non-exclusive sense of "or". The exclusive "or" (either a or b but not both: "xor") can be represented by the symbols "⊕" and "⊻".