How does one tell? There isn't always a permission statement even in videos that have been left peacefully in place for years.

Also (from Wikipedia):

"Since Viacom filed its lawsuit, YouTube has introduced a system called Video ID, which checks uploaded videos against a database of copyrighted content with the aim of reducing violations.

In August 2008, a U.S. court ruled in Lenz v. Universal Music Corp. that copyright holders cannot order the removal of an online file without first determining whether the posting reflected fair use of the material. The case involved Stephanie Lenz from Gallitzin, Pennsylvania, who had made a home video of her 13-month-old son dancing to Prince's song "Let's Go Crazy" and posted the 29-second video on YouTube."

Many copyrighted songs are clearly tolerated by their legal owners if they link to a popup ad that offers a chance to buy the songs legally from a downloading site. I don't think you need to worry about any like that. On the other hand, to have an ad pop up in a religious service seems a bit jarring, so I would suggest not restricting yourself to those. They may perhaps never be used, though it would still be interesting to know about them.