I’m looking for the correct way to say “made by” or “created by” for a custom garment tag. I have heard of "fecit" coming after a name but I’m thinking about bookplates and the “ex Libris” header as the inspiration. Is there an equivalent for this phrase?
In early modern Europe, the common phrase was ex officina (from the workshop), followed by the establishment's name, either in the genitive or as an adjective.
I think a practical way of implementing this in a modern, non-Latin-literate context is to put ex officina but keep your name or the name of your company in its normal form.
As you mention, probably the oldest phrase for this would be [name] mē fēcit: literally, "[name] made me". (In each of the examples below, the first line is a direct transcription of the original, the second line is a translation/adaptation into standard Classical Latin, and the third is an English translation.)
The oldest attestation for this phrase is on the Praenestine Fibula, from the early seventh century BCE:
MANIOS MED FHEFHAKED NVMASIOI
Manius mē fēcit Numasiō
Manius made me, for Numasius
This remained popular all the way through the High Middle Ages:
This is from the south portal of the Church of Santa María la Real, in Sangüesa.
MARIA MATER ΧΡΙ[ΣΤΟΥ] / LEODEGARIVS ME FECIT
Marīa, Mater Christī / Leodegarius mē fēcit
Maria, Mother of Christ / Leodegarius made me
Sometimes the inscription was varied or elaborated further, with forms like [name] artifex mē fēcit, or [name] fēcit hoc. But fēcit seems to be the verb form of choice. This page lists some more examples.