hashtag, n. — Green’s Dictionary of Slang

hashtag n.

[the Twitter symbol # [hashtag] used to indicate a subject label]

(US campus/teen) shorthand for the comment ‘further information’, ‘and in addition’ or 'in other words'.

2012		C. Eble UNC-CH Campus Sl. 2011 5: HASHTAG — further information: ‘Some girl in line was whining about her boyfriend. Hashtag. No one cares.’ ‘Grammar is awesome! Hashtag. Suckup.’.
2014		C. Eble UNC-CH Campus Sl. Spring 2014 7: HASHTAG — in other words: ‘I almost didn’t go out, but I rallied. Hashtag. Yolo. Swag.’ ‘I pulled an all-nighter last night. Hashtag. Midterm week’ .