Not to be flippant, but this smacks of an XY Problem, or at least unnecessarily high levels of cleverness. Why would you need to tell the difference?
in reply to Determination of a subs' invocation from within the sub [RESOLVED]
Assuming you have a Good Reason™, one difference is prototype checking. From perlsub:
Not only does the & form make the argument list optional, it also disables any prototype checking on arguments you do provide. This is partly for historical reasons, and partly for having a convenient way to cheat if you know what you're doing. See Prototypes below.
#11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.