Or would that clash with SharePoint Online
Right now I'd argue that since migration the site doesn't even have a name yet, or that it is called "SharePoint Stack Exchange". So you could base your abbreviation on that, e.g. SPSE.
However we do need to decide on a name. We can continue to call it SharePoint Overflow if we want, or come up with a new name more people prefer. (This is loosely covered under point 4 in The 7 Essential Meta Questions of Every Beta and should be discussed in a new meta question.)