The symbol has a variety of names. It could certainly be used without an article. But "a" is not incorrect.
Student or Learner
There is a "#" at the beginning.Doesn't this symbol "#" have one of its written words spelled "octothorpe" and starts with a vowel sound? So, why has only the indefinite article "a" been used? Can it be preceded by both limiting adjectives "a or an" if I write it symbol? Would it be good to leave it a zero article?
I call it a "hashtag" so I would use "a" before it. However, I would not actually think about the name of the punctuation mark if I was writing that sentence. I would say, for instance, "Don't put a '!' at the end of your sentence". I would simply be thinking of the symbol. I wouldn't think of it as "Don't put an exclamation mark at the end of our sentence".
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.
I think you could search far and wide and not find anybody who has ever heard the word "octothorpe."
Pound sign or number sign would be the most common (before Twitter made "hashtag" a common thing). It's also a sharp mark in music.
In BrE, it's hash not pound, except the Twitter hashtag usage. I have only come across octothorpe in discussions on language forums on the topic- I haven't come across it in the wild.
Last edited by Tdol; 03-Jun-2014 at 15:10.