For anyone else interested where it comes from. I haven't seen it mentioned elsewhere unfortunately.
Have we found "SFOTSE" being used in the Roman period? Seneca was popular, and it became a well known phrase
Moral letters to Lucilius/Letter 25 - Wikisource, the free online library
QuoteI must insert in this letter one or two more of his sayings:[2] 5. "Do everything as if Epicurus were watching you." There is no real doubt that it is good for one to have appointed a guardian over oneself, and to have someone whom you may look up to, someone whom you may regard as a witness of your thoughts. It is, indeed, nobler by far to live as you would live under the eyes of some good man, always at your side; but nevertheless I am content if you only act, in whatever you do, as you would act if anyone at all were looking on; because solitude prompts us to all kinds of evil.
Epistulae morales ad Lucilium/Liber III - Wikisource
Quoteait Epicurus, cuius aliquam vocem huic epistulae involvam. [5] 'Sic fac' inquit 'omnia tamquam spectet Epicurus.' Prodest sine dubio custodem sibi imposuisse et habere quem respicias, quem interesse cogitationibus tuis iudices. Hoc quidem longe magnificentius est, sic vivere tamquam sub alicuius boni viri ac semper praesentis oculis, sed ego etiam hoc contentus sum, ut sic facias quaecumque facies tamquam spectet aliquis: omnia nobis mala solitudo persuadet.