I always write Perl constants as BIRD(). Perl constants are subs and trying to hide this fact from yourself really isn't doing you any good in the long run, IMHO.

There are lots of other places where barewords lead to potential ambiguities so I've found that the practice of avoiding barewords even in some places where Perl won't even warn about them can prevent misunderstandings between me and perl.

At work we have a coding standard that requires literal hash key strings to be quoted. That is, $hash{foo}= { bar => 'baz' }; must instead be written $hash{'foo'}= { 'bar' => 'baz' };. This is actually one place where I personally violate my own 'no barewords' general principle. I used to follow a similar (personal) coding practice until a while after Perl changed the rules such that "hash key 'context'" became unambiguous (all barewords are quoted now; earlier only some barewords were quoted).

These days I'm comfortable using barewords in "hash key 'context'". But part of the reason that I am is that I never write just shift nor just CONSTANT_NAME (etc.) but instead shift @_ and CONSTANT_NAME() so I don't get burned by "hash key 'context'" now being unambiguous.