In or near an area of restricted visibility, whether by day or night the signals prescribed in this Rule shall be used as follows... (list of rules)

But they are superseded by:

(i) A vessel of less than 12 meters in length shall not be obliged to give the above mentioned signals but, if she does not, shall make some other efficient sound signal at intervals of not more than 2 minutes.

"Hey, don't hit me" At the top of my lungs???

So while I have no definite requirement for a bell... I do have to make a sound at intervals of "not more than 2 minutes..." and my little can of "air powered horn" probably wouldn't last too long... and as someone said... "they look salty."