How do I solve 3 down in Times Cryptic 29549?

Question

Accepted Answer

3 down reads "Check written without a pen" (3 letters); the answer is STY. It's a deletion clue: start with a word the clue points to, then drop one or more letters. Indicators include 'endlessly' (lose the last letter), 'beheaded' (lose the first), or 'heartlessly' (lose the middle). The full step-by-step breakdown is on this page.

Check written without a pen (3)

3D — Check written without a pen (3) — STY