Hi Becky.
I doubt I'm going to solve the mystery but I'd put a few bob on that NOT being a Pentax as (a) it doesn't look like any I've ever seen (and I've had a K1000 and a few of the true K-mount lenses some years back) and (b) I'm pretty sure Pentax put(s) its name onto everything it made (makes). My guess would be an independent of some sort and probably a pretty unknown one as the likes of Tamron, Sigma, etc all mark their lenses somewhere.
Thing is, does it work / render okay? If so, no problem - neither the camera nor the film will care.
Hope it works for you.
Regards,
Paul.