Strange lock screen;looks like music note and says "advertisement"

Pretty sure that this is simply caused by some media that got played on the phone. Probably a video which started playing automatically in Facebook or on a website. And, yes, it was most likely an ad, hence the word "advertisement". I get this from time to time. It hangs around if it was the last piece of media you played. It clears the next time you unlock the phone, or the next time you play some media.

Hi. Is it the Connect to iTunes screen shown in this link: https://support.apple.com/en-us/HT203122? If so, you need to follow the instructions to restore the phone.

Was it ever jailbroke?

Was it modified to do things that Apple did not intend it to do?

Good call.

Take a screenshot and post it here.

Take your phone to an Apple Store.

Hi,

Does it look like there is music playing on the phone? with a pause next, previous buttons near the top of the screen?

I would say it again, an apple store appointment is your best bet.