Spotted on the Train: January 13, 2015

 Someone thinks they remember their grammar lessons.

From wikipedia:
Stet is a form of the Latin verb sto, stare, steti, statum,^[1] originally used by proofreaders and editors to instruct the typesetter or writer to disregard a change the editor or proofreader had previously marked. This usage of the verb, known as the "jussive subjunctive",^[2] derives from the active-voiced third-person subjunctive singular present and is typically translated as "Let it stand".^[3]

Conventionally, the content that included the edit to be disregarded was underlined using dashes or dots and stet written and circled above or beside it.^[3] Alternatively, a circled tick or checkmark could be placed beside the content in a margin.^[4]

Found via Google Image search on STET

~photos by iTouch