That really shouldn't even be visible, and if that type of annotation is used, it should be a picture in representation (apparently a mouth). Ignore it, just know the text wasn't typed but input in some other way.
If you care more, a lot of sites are starting to use propietary icons for advertising origin instead of using a unicode map, thus the icon has no target on the client and this is really a bad look for whichever sites are starting to do this (it's lockin tracking, and no surprise from FB). You see, it will be known if that object links to some sort of picture, thus if it links to a picture of propietary origin, it can be used for identity tracking to that origin. This has been done for decades with a 1x1 pixel image in e-mail, which if the image is revealed, a link is followed from you to its home (thus never enable images in email by default). The "OBJ" you're seeing is a icon basically stating that you're being protected from tracking (barely). Facebook, Amazon and Google are absolutely horrible at this, and Facebbok in particular is always trying new ways to track you (Amazon and Google are already cemented in.... for now).
In short, be happy you're seeing that OBJ (but you might not for long). Although Apple and Firefox seem to be on a rampage lately to stop trackers.
) a lot in Facebook posts lately - usually at the end of a sentence.
