I'm digging through some old photo equipment that my grandfather recently gave to me. I just came across a 52mm Nikon lens filter, labeled 'LlBc' (that L L B C, but it's case sensitive). Does any one have any idea what that is?
That's actually an L1BC filter (ell one bee cee). It's equivalent to a Skylight 1A, and is meant to cut UV with film. It's of very limited use with digital; primarily to reduce blue-channel overexposure at high altitudes. With colour film, particularly transparencies (slides), it's a slightly more aggressive version of a "clear" UV filter useful when the blue sky is the main source of illumination. In other situations, the pinkish tone can be problematic.
It's likely that you're not reading the filter correctly. It's probably L1Bc. It's a skylight / UV filter used in the film days. It has a very slight pinkish cast.
It has no value when used with digital cameras. If you want to use a UV filter on DSLRs, current inexpensive UV filters are clear (don't have a color cast).
This filter really only has value if you're shooting film, and want to try to replicate older techniques (and color tints) as much as possible.
From Nikon's support page Using Nikon filters with Nikon DSLRs,
The multilayer coated Skylight L1BC also cuts UV light and is often left on the lens to protect it. The Skylight L1BC may affect color balance due to its slight pink color.
The Nikon L1BC is a multicoated Skylight + UV filter. This filter is multicoated. The coat on lenses and filters mitigates reflections. Thus the filter passes more light than a non-coated filter. The coat also mitigates flare by curbing reflections from the polished lenses behind. If not checked, these misdirected rays commingle with the image forming rays. This causes flare that induces a contrast reduction. The coat must be ¼ wave length thick. That makes it color specific. The fact that this filter is multicoated means it is designed to mitigate several different colors of light.
A plain UV is practically colorless. A Skylight filter is colored slightly pink. They were very popular in the days of film cameras, particularly so when the film being used was a slide film. Slides tended to display shadows as being bluer than expected. This is because sunlit scenes usually are illumined by sun and scatter light from the blue sky. Photographers were bothered by fact that shadows were tinted blue due to this scatter light. The Skylight filter corrected this fault. Keep in mind, a slide film is what it is, and in that era, no software to correct. Again, the Skylight was popular plus the UV portion cut haze. Haze is present in distant landscape views and aerial photography.