Not sure if this applies. But if you lie down on a bed, most manufacturers will put bed sheet tags on the bottom right of your sheets. I always removed those tags like shirt/jeans tags but now it gives you a starting point putting on fitted and loose sheets. Sorry I just became an adult at the age of 42
Another option which I do is use a permanent marker to put an indication on the sheet label (I go for “↕ side” and “↔ top”, but whatever works for you).