You see and hear a lot of different titles in Japnaese martial arts. Unfortunately, a lot of people have little or no idea how these titles and honorifics are actually used. I’ve seen people addressed as “Smith Sensei,” “Bob Sensei,” “Sensei Smith,” and “Sensei Bob.” I’ve also seen people insist on being address as “Hanshi,” “Shihan,” “Soke,” “Shidoshi” and “Shidoin.” In Japanese budo culture, only one of these is correct.
Being introduced as Sensei is fine. Introducing yourself with a title sounds either ignorant of Japanese usage or extremely arrogant, as if you are giving yourself some sort of title. If you are introducing yourself, it’s just „Peter desu“ or „Lowry desu“ Anything more is arrogant or foolish. Even the very senior shihan of my acquaintance just introduce themselves with their names. Their business cards will have their ranks and certificates, but that’s all, no honorifics. Those are are something other people use to talk about you, not something you use for yourself. Certificate titles like “shihan” or “shidoin” aren’t forms of address either.
“Sensei” isn’t a title. It’s an honorific like “Mr.” or “Mrs.” In English it would be a little strange to introduce yourself by saying “I’m Mr. Boylan”. It’s even stranger in Japanese where the honorific a person uses to address you depends on your age, position relative to the person addressing you, the particular situation and your relationship with them. I have been addressed as everything from “kun” (a diminutive used to show that I’m a lot lower status than the speaker), to “san” (the general honorific used for people of relatively equal status), to “sama” (shows great respect and implies high social status).