The FAA AIM says:
The fact that a straight−in minimum is not published does not preclude pilots from landing straight−in if they have the active runway in sight and have sufficient time to make a normal approach for landing. Under such conditions and when ATC has cleared them for landing on that runway, pilots are not expected to circle even though only circling minimums are published. If they desire to circle, they should advise ATC.
So Lantirn is correct about that. However, the original question was:
What should I understand from "clear for straight in app"?
The answer is as per the first reply: do not carry out the procedure turn.