Tch
From Teflpedia
Tch is an English consonant trigraph consisting of the letter T plus the consonant digraph Ch.
This is always found in coda position; never found in onset position.[1]
This reliably represents unvoiced palato-alveolar affricate /ʧ/ sound. More so in fact. The French pseudo-Anglicism tchat is sometimes used in French to distinguish the English loanword meaning of "(Internet) chat" /ʧæt/ from its French homograph 'chat' /ʃa/ meaning cat.