The trainer from Umamusume, depicted with a capital "T" for the head, similar to the T-head Admiral seen in Kantai Collection art (and Idolmaster's P-head Producer). The "T" is derived from the first letter of "Trainer". A similar example is a trainer whose face is a T (or a T-shaped mask) as opposed to the entire head.
There is another related character, the To-head Trainer. This is like the T-head Trainer, but with a ト (Japanese katakana "to", from the first kana of toreenaa/"trainer") instead of a T. As it still starts vocally with a T (and may resemble a "wide T" turned 90 degrees onto its side to English readers), it falls under this tag too.