Register Your Trademark Immediately
When you want to register a trademark, it is late to wait even for a second. You should do the registration quickly, even if your business is a newly established startup. For any kind of reason, someone may register your intended name before you do. The law says anyone who brings the name sooner for registration will be accepted. If I tell you I've been using this trademark for the past five years, I may get results, but it will be a very complicated and long process if you want to be more successful than the one who filed a registration before you.
You have heard of the name Haida Sandwich in Iran. Someone has registered Haida in Toronto and it has nothing to do with that Haida in Iran. The owners of the Haida trademark in Iran can't simply take their trademark back from those in Canada. Haida is even registered in the US, which also has nothing to do with the original brand in Iran.
You should notify everyone immediately after you register a trademark. Notify everywhere, in catalogs, on websites and anywhere you can publicize your product using any method possible, so it would be seen more and everybody would know that the trademark belongs to you.
It is possible that someone requests the same trademark while your request is being processed. In that case, the one who has requested sooner will be processed first.