The marking of this box only indicates that the distribution is from an IRA, not what type of IRA. Your account statements and Forms 5498 from the account will indicate whether the account is a SIMPLE IRA, a SEP IRA or an ordinary IRA.
SIMPLE and SEP IRAs are IRAs to which employers make deposits. If the IRA has received nothing but personal contributions that you yourself deposit or is a rollover IRA established by rolling over to it an employer plan like a 401(k), it's an ordinary IRA, not a SEP or SIMPLE IRA.
