° in Axe is very much like & in C. EXP→X stores some value into some memory represented by "X". Where is this memory you ask? Why at the address °X. This means that EXP→X is actually the exact same thing as EXP→{°X}ʳ. In fact, X and {°X}ʳ are completely interchangeable for any access to the variable X.

One use for this is to sign extend a byte located in X. Axe has a signed{} command, but that requires an address to load from. The solution is to use signed{°X}.

Another use (which, oddly enough, I can't seem to find in Commands.html) is for creating named variables:

EXP→°AB creates a variable called AB which can be used just like variable A, etc, and is stored at the address EXP.

An example showing both uses is °A->°AA which creates a variable called AA which aliases (always contains the same value as) A.