Found here.

If one is trying to politely but firmly get a point like this across, using a smiley or unnecessarily-cutesy text-speak comes across as very disingenuous, even passive-aggressive.
It really reminds be of one of my favourite blogs, Passive-aggressive notes. I don’t know why they crack me up so much; maybe I can identify with pent-up frustration. I also like the last minute apostrophe in this photo – clearly an after thought but at least this person is trying.