Why?

looks like a virus is on your computer or your just clicking on some harmful ads. Does this happen to you on other websites?
do a virus scan with your choice anti-malware program. I usually use malware bytes for this.

aah, no. i use ublock.
i hate when sites do that. as much as i want to support them theyre pretty much forcing me to block ads. i feel like all the sites i go on have been having this problem recently too! since having to scan for malware is a pain in the butt i just keep the adblock on.

 also, id reccomend scanning your computer if its happened repeatedly.

Ok, I just set my antivirus to scan for malware. This has happened once so far on my desktop I think, but it was a while ago and nothing bad has happened. usually I'm careful about this stuff XD

The same has been happening with me and my computer is finding no viruses or anything. I've only had it happen in OTD.

Ok, scan finished. Nothing.

It's happened on The Cats, but it just happened on OTD.

that was one fast scan, what antivirus did you use? 
I'm telling you now, get malware-bytes it'll help you in the long run.

If it was adware, wouldn't it also do it on facebook and other sites?

oh yeah.
Seems like a forum issue then, I haven't been getting anything so far.
We'll see if the problem persists with others.

Am I the only one without any Adblock or PB+ that isn't having any problems?

Am I the only person not seeing OP's SN?

I can see it.
It might be because you're on a device that isn't able to read whatever characters make up OP's sn. When I'm on my ipad/phone, sometimes I can't see certain sn's because they're in a fancy font and my device won't load those characters. But on my laptop I can see everything.
If it's not that, then idk why you can't see it.

probably because it's special characters and you're on the mobile version.