New technology always introduces linguistic challenges. In the early days of movie making, it wasn't clear what these new entertainments should be called. Kinesigraphs (after photograph)? Films? Moving pictures? Motion pictures? Picture shows? Movies? It is possible to imagine a new concept in different ways. Do you name it for the thing that distinguishes it from what came before? (It's a picture — but it moves!) Or for the medium it's printed on? (Film, itself an extension of the "thin layer" image.) It will take some time for people to converge on a favorite, sometimes a few generations.
The process is no different for the coinage of new terms in ASL. When a new idea comes into the culture, signers can borrow from English (through finger spelling), modify an existing sign, or come up with something new through a reimagining of the concept. For example, here are two different possible signs for photobomb:
The one on the left conceptualizes it from the point of view of the picture-taker — someone pops into the picture I am taking. The one on the right conceptualizes it from the point of view of the person having their picture taken — someone barges in while I'm being photographed.
This gif comes from a story at Hopes&Fears that asked a pair of deaf signers, Douglas Ridloff, an ASL artist, performer, and educator, and one of his students, 12-year-old Tully Stelzer, to give their signs for new terms.
For the term onesie, Ridloff gives the sign form "pajamas," while Stelzer uses the concept of putting something over the body in one big piece.
If these concepts stick around long enough in the culture for the community to discuss them frequently, eventually the community will settle on a stable sign. Already Ridloff reports that people in the deaf community don't like his "photobomb" sign because they find it awkward. If we are still talking about photobombs a generation from now, only then will we see what the proper dictionary sign turns out to be. It may well turn out to be Stelzer's. In any language, change tends to be driven by the younger generation. Who says "moving picture" any more?
See signs for "emoji," "food coma," "selfie," and others, and read a Q&A with Ridloff and Tully about their signs at Hopes&Fears.