Usernames for either people, brands or products all have to follow the exact same rules:

1. No Spaces.  Your username has to be one word, such as “cocacola” instead of “Coca Cola”.
2. Only letters and numbers.  You can’t cheat the first limitation by using underscores or hyphens in the place of a space.  There actually is one notable exception — Twitter does allow underscores in usernames, but 99.9% of all social networks only allow letters and numbers in the username.
3. No punctuation or other non-alphanumeric characters.   There are no social networks which allow apostrophes such as “McBrady’s” or anything other than just plain old letters and numbers.
4. Capitalization is Irrelevant.  For purposes of searching for a username, CocaCola and cocacola are identical.

These are not requirements we set, they are limitations dependent on how Social Media websites handle usernames.  Usernames in social media comprise what we call “vanity URLs”.  A vanity URL is a website address like https://twitter.com/knowem.   Just about all of these rules of username searching are in place because of the naming constraints on how web servers handle URLs.  URLs with spaces and apostrophes are confusing to web servers, and so they’re not allowed in usernames.

More information can be found here: How to Search for Your Brand or Username on Social Media