The internet search engine seems not to recognize it, so I cannot search for it there! I had assumed it was "augmented" but am now very unsure. Thanks
More specific to the question of what the degree sign means is that yes it is a diminished chord and that means that the chord has the notes that form a minor third from the root and a diminished fifth from the root.
So, as Tim mentions, in this case, it will be F#, A (minor third) and F# to C (diminished fifth)
Different editors/publishers seem to notate certain chords differently, but a fairly common scheme is to describe an C diminished triad (C-Eb-Gb) as C(b5), an C half-diminished 7th (C-Eb-Gb-Bb) as Cm7(b5), and a C full-diminished 7th (C-Eb-Gb-Bbb) as C°. Note that a C full-diminished-7th is enharmonically the same as a diminished triad with an added major 6th (C-Eb-Gb-A), and because it would be weird to describe a note nine frets up as a "seventh" (rather than a major sixth) but it would also be weird suggest that the top two notes of the chord are only separated by a second when they're three frets apart, using the C° notation is a simple way of saying that chord note contains pitches that are spaced upward at intervals of three frets starting at C without having to worry about what those notes should be called.