A more efficient way to denote am or pm
Humans have, over time, abbreviated the terms for denoting morning and evening when referring to a specific time. As our schedules and devices get more complex, there is an advantage to simplifying the text necessary to communicate information, as evidenced by the abbreviations used in texting.

The logical progression suggests that we go one step further and delete the M in AM & PM. That M is useless. The letter does not clarify the time of day nor does it enhance the message. Just as we got used to A.M. instead of ante meridiem, we will get used to the a & p. It allows graphic information to appear neater and more concise and works well in both upper and lower case.

Here is a typical email format:

Notice how awkward and clunky that capitalized AM looks. It draws attention to itself and it's not even very important. So, when I can, I change the AM to just the a:

That is clearer with fewer unnecessary words. But, heck, while I'm at it, I often even delete the other superfluous characters and words:

I checked the Email Settings menu on my devices - phone, pad, laptop - but there is no option for abbreviating am & pm. But, in iTunes, I was able to change to the single letter:

Examples already in use

Concept: early 1990s
Research and exploration: 2010, 2014