Are you saying the actual text "Ad info" us showing, or that information from an ad is shown? In either case, I've never seen this on any of my Roku devices. Does this happen on any particular channel?
If this is a separate Roku device, rather than a TV with Roku functions built in, could this be something the TV is displaying rather than the Roku?
Do you still see it with the TV set to other inputs?
Roku Streaming Stick +, 3810X, Ser YH0059427035, wifi - Samsung UN55ES6100
Roku Streaming Stick, 3600X, Ser 5S56D8240827, wifi - JVC EM37T