[Constitution Day]

If you mean the "rising sun" flag, that is still used by the Japanese Maritime Self-Defense Force (MSDF) (a.k.a. the Japanese Navy) today.

Here is an article from 2007 with a photo:

Taking Off With the Japanese Navy

I can't post the photo here as it's from Getty Images.

[Radl]

Yes. I don’t know where I heard it but I was under the impression that after the war it was not permitted to be flown, just like the NAZI flag.