The desire for people to label themselves for your convenience is a sign of laziness, obviously - but it also smacks of a healthy (or unhealthy) sense of self-superiority and self-entitlement. I’m not sure if it’s possible to do this without dehumanizing and hating the people you are doing this to.
The normal/rational approach to this sort of question is to either ask, if it doesn’t come up much, or to post a sign, if it’s a standard condition that applies to all. Like, posting a sign “no pregant women in our pool”, or wearing a sign around your neck, “I distrust and hate people who adopt or are adopted.” It’s not normal to expect everyone else to wear signs for your benefit - and it’s not even rational to expect it when your particular hangup is so ludicrously unique as the OP’s. Everyone has hangups, and if we expected people to post everyting about them that could possibly bother anyone (even crazy people), then they’d have to post every single fact about themselves, from their entire ancestry to their complete medical records to their rated taste preferences for every food in existence. In short, expecting this is stupidly insane, and speaks of titanic ego to think that your personal hangup is so much more important than everyone else’s that it deserves everyone else giving it special consideration.
If the issue was larger, both in the number of people who are sensitive to the property and the degree to which it’s a problem if a sensitive person encounters the stuff, then voluntary or mandatory labeling may occur for the few properties that have that large an impact. Some examples of this are the labeling of kosher food, peanut contamination, or carcinogens. The thing is though, there has to be some real potential damage in enough people’s minds to make the labeling mandatory, on the products which are ‘unclean’. For concerns that are not so severe/widespread, you get voluntary labels that mark ‘clean’ products, rather than mandatory warning labels.
To require mandatory warning labels on people, rather than products, is even more dodgy. As noted, for a warning to be mandatory it means that the property in question is reviled. It’s the difference between people choosing to wear a cross to advertise that they’re Christian, and forcing them to wear crosses (or scarlet letters, or stars of David) so you can know to treat them predjudicially.
That aside and regardless, to expect people to warn you when they were adopted without you having to go to the minimal effort of asking them at least presumes that you think that lots and lots of lots of other people have this peculiar strong hangup with adoption too. If you believe this, they either you’re not living in the USA, or you’re frighteningly oblivious to the culture you’re in.