I saw this on the back of a bank-by-mail envelope from my credit union.

Problems:
An apostrophe is missing from the contraction, and the verb used as an adjective should not be capitalized.

Explanation:
Whoever wrote what is printed on the back of the envelope was trying to use the contracted, everyday-speech form of “I am”.

Unfortunately, the contraction “Im” lacks the required apostrophe.

I believe that this is consistent with my “Devolution toward Simpler” hypothesis.

It’s simpler to write “Im” than to write “I’m” (two keystrokes vs. three keystrokes).

I also believe that the increasingly common practice of dropping required apostrophes has been influenced by people’s experience with text messaging.

• Given the typical limit of 160 characters in a text message, every character is precious, so dropping required apostrophes seems to many like a reasonable price to pay.
• Also, text messaging on most cellular telephones, which don’t have full QWERTY keyboards, is tedious, so dropping required apostrophes lets users of the simpler phones avoid this tedium.

The other problem is that “Save” — a verb used as an adjective to modify “envelopes” — is capitalized when it should not be.

Unnecessary capitalization has become another common English blunder.

I see this unnecessary capitalization more with nouns than with adjectives.

Maybe American English is becoming more like German, or maybe American English speakers are losing their confidence in how to capitalize and therefore randomly capitalize words that don’t require it.

Solution:
“I’m out of save/pay-by-mail envelopes.”