The B9100 is a short link road in Montrose, a mere shadow of its former self, and that was never much of any importance. Owing to its short length its history is not fully known but it presumably gained its number around 1930 before losing most of its length when the A92 was rerouted around 2000.
The road originally began at the south end of Montrose High Street when this was still part of the A92 and then followed George Street into Ferry Street to reach the harbour. Today, however, it starts at the crossroads between Ferry Street and Commerce Street, and heads south into the harbour. Of the four arms of the crossroads, north and east are now unclassified, whilst west is the B9133; this raises the question of why two numbers are still used, but then again both routes are unsigned and rarely shown on maps, so why not?