TJ in pet registries is almost certainly an initial combination rather than a standalone name — the kind of entry that results when an owner writes their pet's initials in the name field of a licensing form. At rank 1030, with 114 recorded registrations, it has enough frequency to be real, but the interpretation of what those registrations represent is more complicated than for most names on this list.
The Initials-as-Name Pattern
Using initials as a pet name is genuinely common — particularly in certain regional and generational traditions where two-initial names like TJ, CJ, and AJ are given as actual names to human children (think TJ Maxx founder, or TJ as a standalone on baby name charts in the 1980s and 90s). So some of these registrations are owners who genuinely named their pet TJ. Others are likely abbreviations entered into the name field on a form.
Functionality as a Pet Name
Two sharp consonants with no vowel runway make TJ a distinctly functional pet name — you can say it loud and short, which works. It's in the same phonetic territory as Rex or Ax for projection. The name reads as casual and no-nonsense, which fits the owner profile of someone who doesn't want a lot of naming ceremony.
Paperwork Considerations
If TJ is the intended name, register it as written — but be aware that some veterinary software handles two-letter all-caps entries inconsistently. The human version TJ exists but is not widely tracked in official naming databases, which reflects its informal-initials origin rather than a gap in usage.