Time for a test:
(1) You need a bridge opening to make your passage. What's the best way to get a lift?
a. Sound one long horn blast followed by one short blast
b. Call the operator on channel 13 VHF
c. Raise and lower a white flag
d. All the above
(2) Which is the Puget Sound bridge pictured above?
a. 16th Avenue S. Bridge, South Park, Seattle
b. E. 11th Street Bridge, Hylebos Waterway, Tacoma
c. Ballard Bridge, Lake Washington Ship Canal, Seattle
d. SR 529 Bridge, Ebey Slough, Marysville
(1): All are legitimate signals. However: some bridges use sound signals that differ from the mostly-used long/short; in Seattle, at least, rec boaters are discouraged from using channel 13; the white flag is a legitimate request signal…but rarely used and a less vigilant operator might miss it. The takeaway---plan your voyage well beforehand and add bridge and lock characteristics to your study of local weather and currents, shipping lanes, available harbors, etc.
(2): b., Hylebos. (the Ebey Slough bridge is a fixed bridge. Even if it appreciated your signal, it couldn't open.)