Placed along the road to Pu'uhonua O Honaunau National Historical Park. "Speed limit 45 MPH".
You should not need an additional hint. If you need a hint, beware that the hint is actually exact instructions.
Zntargvp. Vafvqr onfr bs lryybj 45 zcu fvta cbfg. Cyrnfr ercynpr nf sbhaq.