Inland navigation rules require a power vessel anchored in restricted visibilty to sound which signal?

This answer depends greatly on the size of the vessel at anchor.

Rules of the Road. RULE 35,SOUND SIGNALS IN RESTRICTED VISIBILITY

(g/f) A vessel at anchor shall at intervals of not more than 1 minute ring the bell rapidly for about 5 seconds. In a vessel 100 meters or more in length the bell shall be sounded in the forepart of the vessel and immediately after the ringing of the bell the gong shall be sounded rapidly for about 5 seconds in the after part of the vessel. A vessel at anchor may in addition sound three blasts in succession, namely one short, one long and one short blast, to give warning of her position and of the possibility of collision to an approaching vessel.