May be serifed I?
Many sans serif typefaces have these slabs even on the letters like i, j, l and 1 as well. There must be some terminology.

I don't think there is a term specifically for this, and perhaps there should be. Many all-caps comic fonts have both kinds, so that the serifed I can be used for the personal pronoun "I" while the plain I is used in other words; I believe Charles Schulz was the first to adhere to this practice consistently in his hand lettering.

According to David Berlow, those faces are some-serifs.
Another related thread: How does the serif on a sans-serif i increase legibility/readability?

"barbarism" sounds a bit too negative :-)

"They are serifs."

Nah, that's too obvious. If there's no term, then we need to invent one. ;o)

So, to be clear, I think what we're looking for is a word for "a serif that is thought of as a normal feature of a character even in an otherwise sans-serif context."

I suggest something like obserif, short for obdurate serif (or obstinate, or even obligatory).

I work with a lot of educational publishers (where this comes up often re: the whole 2nd-grade letterform split), and editors usually mark it up as a "serif I". Granted, editors might not be the best people for naming these things, but at least we understood them.

Drunk I's ? -- always what happened when I went to a bar & stayed a while.

"What do you call an 'I' with bars?"
A selfish person you can reach on a cell phone.

What do you call an ’I’ with bars?

Transerif?

So 'I' walk into a bar, and announce: "There's a new serif in town".