Modern iteration: 谢^2
Chinese traces use of the iteration mark (usually〻 or 々) to indicate a repeated character back at least 2900* years or so. A Wikipedia article dates this piece of bronzeware
back to 825 BCE, where you can see something like 二 used to indicate doubling of 子and 孫 to make “子子孫孫寶用”
So in the modern era, why not 字2? Thanks to Transliterationisms for sending 谢2 over from I’m guessing Taiwan:
It doesn’t mean much that I don’t remember seeing this before, since I don’t get out much. But it does make me wonder if anyone’s got other shorthands they’ve seen in the wild.
* Originally calculated as 1900 years — revealing the effectiveness of my undergraduate degree in mathematics.