I's

From I +‎ -'s (suffix forming plurals).

I's

1. plural of I (letter of the alphabet)

• Opinions vary regarding the use of apostrophes when forming the plurals of letters of the alphabet. New Fowler's Modern English Usage, after noting that the usage has changed, states on page 602 that "after letters an apostrophe is obligatory." The 15th edition of The Chicago Manual of Style states in paragraph 7.16, "To avoid confusion, lowercase letters ... form the plural with an apostrophe and an s". The Oxford Style Manual on page 116 advocates the use of common sense.

• i's

From I + 's (contraction of is, has, and was).

I's

1. (nonstandard, dialectal) Contraction of I is.

   I's going now.

2. (nonstandard, dialectal) Contraction of I has.

   I's got to go.

3. (nonstandard) Contraction of I was.

   I's going to the store yesterday.

• i's (eye dialect version of it's (it is), rather than I is, but is often written the same as I's because it is at the beginning of a sentence.)

From I +‎ -'s (possessive marker).

I's

1. (nonstandard) Synonym of my

   This is my husband and I's favorite place to sit.

• When "I" or "me" is used with a conjunction, it is often advised that it is better (more polite) to refer to oneself last. Thus it is more common to say my husband and I than I and my husband. In such cases, the prescriptive rule is to use the same case form one would use if there were only one pronoun, thus my husband and I for a subject of the verb rather than the more colloquial me and my husband.
• I's is a result of adding -'s to the whole noun phrase rather than, as would traditionally be done, using my; the Standard English way of expressing the usage example above is, This is my husband's and my favorite place to sit.
• Compare also your guys's and similar nonstandard but widespread forms.

• s͞i, Si., S. I., SI, S.I., si, Si