Thanks for asking, though. It has to do with my research. Specifically, it relates to an effect called gravitational lensing.

Basically, in general relativity, the presence of a gravitational field causes light rays to "shear," meaning that they spread in one direction and compress in the orthogonal direction.

The sphere shown in my avy represents something called the "celestial sphere." This is basically the mathematical representation of what someone sees when they look into the sky. If you collect all the light rays that cross a given point in spacetime (at which point they could, for example, enter somebody's eye), then this collection as a whole is mathematically a sphere, the sphere on which the stars appear to be attached, so historically it's called the celestial sphere. (Strictly speaking, the picture is actually drawn on something called the "anti-celestial sphere," I guess because I prefer to be anti-celestial, but the distinction isn't particularly important.)

So this sphere represents all the directions from which a light ray can enter an eye. If there's a gravitational field in that vicinity, then it will shear the light rays, as I mentioned above. Interestingly, light rays from different directions are sheared in different ways. So if you trace out the plane along which the light rays are stretched by the shearing, as a function of the direction from which they came, you produce a pattern on this space of light rays, and it looks kinda like a fingerprint on the sphere. This is called the "fingerprint pattern" of the gravitational field, and it turns out to be a very effective way to characterize the essential structure of a gravitational field at a point in spacetime in general relativity. In particular, the "singularities" of the pattern, points where the curves fold up on themselves (two are visible in the picture: one slightly down and to the left from the center, and the other up near the north pole) frequently come in precisely the same patterns on finger-fingerprints, but in the case of a gravitational field they define the "degeneracies of the principal null directions," which in turn define precisely what kind of gravitational field you're dealing with. So like detectives analyze fingerprints to identify a person, a physicist can analyze a fingerprint to identify a gravitational field.

When I first put up that avy, I included a few of these buzzwords in my sig, but I quickly decided that'd be too nerdy. But in a thread like this I figure I'm safe.