I have a twitter account for my business, which is @VanOD_ I've never liked having an underscore in the username but it seemed the only option to get a short relevant name when I was choosing. I'm considering changing it to @VanODBristol to include the name of the city I operate in. This does make the name a bit long long but I'm thinking it might help a bit with SEO signals as I'm trying to rank for "man with a van bristol". I'd be interested to hear other people's thoughts whether having a longer username is worth the possible SEO gain, or whether the gain would likely be zero.