Mystery signature found on sculpture! Does anyone recognize this?

Hi folks!

I while back I posted a thread about a sculpture I had gotten from G'ma. (http://able2know.org/topic/326267-1)
The sculpture was mislabeled, and because of the Nature of the work, the provenance, and, of course, the label, we believed it to be the work of Martin Puryear. Here is another link to the piece itself, so you don't have to dig through that last thread:

https://imgur.com/a/9v0JH

However, after another--more recent and more thorough-- examination, we found this small signature incised on the bottom of the piece. It was hidden quite well. Here is a link to the signature:

https://imgur.com/a/oEvWm

Looks like Robert Rust-- or Robert Pust---- I can't tell. Thought one of you folks might be able to. Thanks again for all your help!

DP