No. Gibson is a brand of guitars, why is most likely why it is a copyright tag. If a guitar says "Gibson" on its headstock in an image, I would not see a reason not to add the tag.
This may be a bit biased of me, seeing how I like guitars, but I am intrigued by how various artists draw the aforementioned instrument. I am especially interested in how they would draw a Gibson guitar, be it an SG or a Les Paul.
Well, I digressed there. Anyway, I feel that doing something like gibson_(guitar) may be more appropriate for this issue. The tag would clarify exactly what is it for and would be used appropriately.