It’s 311.
A ‘three-eleven’ is California – or at least L.A. – police code for indecent exposure. Also in Omaha, apparently, as that’s where the band 311 is from and how they got their name.
If it is Naked Day, it should be warmer. I’m waiting for the first of May.
Beltane is quite definitely Naked Day. 
311 is also the American Psychiatric Association’s code for an unspecified depressive disorder.
Which is what you’d get if you went outside naked in the middle of March around here.
sort of like how someone decided to title a show Detroit 1-8-7 even though the Michigan penal code for murder is 750.316.
SoCalization (warning: TV Tropes link)
That trope is the reason why on American TV a character is automatically jailbait if they’re under 18, regardless of the law of the state the show’s set in. Law & Order being a notable exception; being filmed in NYS they use the state’s real age of consent & even use the right name for the different courts.
OK, I’ll play. Right now, underneath my clothes, I’m completely naked!
We’re having a heatwave, so going naked is probably happening all around me. Within closed doors, though, because it would be insanity to go outdoors and have your skin char and flake off your body.
OK, I’ve done my part, but let me tell you, it did not go down well at my office.
I’m jealous of you. I’ve never had the guts to do that. Underneath, I’m fully dressed.
I went one further, I took off all of my clothes…& stepped in the shower.
OK, I’ll fess up. Underneath my pants, I have another, much much shorter, pair of pants.
Section 311 is in the California Penal Code. Though not having anything to do with the law professionally, I own a 1931 copy of the PC which I picked up at a library discard sale.
The California PC was enacted in 1872 and is still in effect, as amended.
yet another reason why I utterly despise the state of California. Especially southern California.