I saw a similar question to this from someone about how to determine their job title, and I felt that my question was different enough to be justified. So here it is:
I have worked as a developer for a small company for several years.
Before that I also did development (though fairly shoddy, as I was very inexperienced) at another company for a couple years.
At my current company I am mostly given assignments with very little oversight, and expected to bring them to completion. I'd say I have a decent amount of knowledge of correct architecture, I can code pretty well, and I've written plenty of stuff on the side too.
Viscerally, I feel like I can justify the title "Senior Engineer" or "Senior Developer", but my company doesn't have formal job titles. I've been updating my resume recently and thinking of looking for a new position, and I'm not sure if I should put developer or senior developer on my resume.
How is this normally determined in a situation like this? Is there any real criteria? I know that HR departments typically have SEII and SEIII for people at about my skill level.
How do I translate this into a title on a resume?
Note: I only do software development and architecture.
EDIT: Also I am self taught - I do not have a CS degree (though I do have a degree, though I doubt that's in anyway relevant).
EDIT 2: Would the question better be titled, "Should I call myself a senior developer or just a developer on my resume"