[JoshTriplett]

'#', by the name "pound sign" and used after a number (like 12#), refers to pounds of weight, not pounds of currency.

[david-given]

Are you sure about that? Pounds weight has its own symbol, ℔ (U+2114, http://www.fileformat.info/info/unicode/char/2114/index.htm if HN won't show it).

I've always known # as representing "number", which is why you see it in lists: #1, #2, #3 etc.

[ghaff]

# after the number is widely understood to refer to pounds (as in weight) in the US. Not sure how common that use is these days but most people would understand what was meant if they saw it.

[mikestew]

Pounds weight has its own symbol, ℔

A symbol that, after many decades of living in the U. S., I'm seeing for the first time just today. In my experience, if it's not written as "lb." or "lbs.", a hash is often used: "#".

[Symbiote]

Draw ℔ very carelessly, and you end up with #.

# is never, ever, ever called the "pound sign" in Britain or Ireland. That's always £.

[SmellyGeekBoy]

I have to admit that possibility did cross my mind shortly after I posted my sibling comment. That said, I've never actually seen it used that way (only ever "lb")