Cartoonist Ryan North wrote me on 9 July about a posting of mine reproducing one of his Dinosaur Comic strips:
… Also, thanks for the shouts out to my comic – I really appreciate it and am also flattered!
North and I both understood this to be an “internal plural” of the composite noun shout-out ‘a favorable mention’ (though that interpretation might not be immediately obvious to all readers; I’ll get to that in a moment). (Earlier discussion of external, internal, and double plurals here — including a somewhat surprising internal plural hards-on for hard-on ‘erection of the penis’.)
You can google up plenty of examples, some with the ‘favorable mention’ sense, some with the sense ‘a public expression of thanks’ (there seem to be still other senses out there), e.g.:
Many shouts out to all the folks I met this weekend at Free Comic Book Day at Comics2Games in Florence, Kentucky! (link)
I only bring this up because I don’t recall many shouts-out to the 24, which is a very cool project run by very cool project … (link)
I wanna give some shouts-out. (link)
Now, the example from North could be understood as having the noun shouts with a postnominal adverbial complemen, and indeed Neal Whitman has argued on his blog that the composite shout-out (however spelled) arose from the noun + adverbial construction by reanalysis, with out assigned to the preceding noun rather than the following adverbial. Along with the reanalysis goes a shift in prosody and a specialization in meaning.
A composite noun shout-out would normally have external plural marking, with the inflectional affix at the end: shout-outs. This variant is hugely more frequent than the internally marked plural (with the inflectional affix on the head of the composite, the noun). But the internally marked variant does occur, for shout-out and at least a few other similar composite nouns, among them sit-up and backup:
IM TRYIN TO GET ABS FAST BUT I WANT TO KNOW IF I SHOULD DO THEM EVERDAY AND HOW MANY SITS UP SHOULD I DO (link)
No matter how many sits up you do if your bf% is too high your abs will not show because of the fat covering them up. (link)
Note: Information Technology conducts regular backs-up of all data stored on enterprise servers. (link)
I have two 500GB FireWire drives in a mirrored RAID configuration, which I use for regular backs up of all my music. (link)
Of course, the standard external plurals are vastly more frequent than the internal ones.