Samsung released a short video that may help you find burn-in marks in your OLED TV. The video should be run on your OLED TV, and it shows a red image that will (according to Samsung) show visible marks if there are any issues in your TV.
If you did find such marks - Samsung suggested to contact a service center - or switch to one of its QLED LCDs... I wonder if this is a mart marketing move as Samsung itself is now committed to OLED TV technology and will start producing QD-OLEDs in 2021. Samsung is probably hoping that no one will remember this video by then...
But this could also backfire right now - in the video comments you can see that many people run the video on their AMOLED phone. Samsung is the world's leader in mobile OLED production and adoption - for smartphones, tablets, laptops and other mobile devices!
Burn-in has been an issue with LG's OLED TVs since 2013 when it first launched these products. In 2018 LG had to replace some OLED TVs in Korea's Incheon airport with LCDs after the OLEDs developed serious burn-in issues, and later in 2018 Rtings.com performed some tests that showed serious burn-in in LG's OLED TVs after only 4,000 hours of use. Last month LG was ordered to compensate two Australian consumers due to OLED TV burn-in.
I personally ran the video my 2016 LG OLEDB6 - and did not see any burn-in at all. UK-based HDTVTest recently performed a 3,700 hour test that shows that burn-in can be avoided if you vary the content displayed in the TV, which makes sense. Click here for an in-depth explanation on OLED burn-in.