"IRA/SEP/SIMPLE" is the name of that box.
If it's not clear whether or not that box is marked, ask the payer. That box should be marked only for distributions from traditional IRA accounts, including SEP-IRA and SIMPLE IRA accounts. For distributions from 401(k), 403(b), 457(b), federal TSP and non-qualified annuity accounts, that box should not be marked.
