If the forum frown at alts, I have seen many accounts that were new but you will noticed they are not new the way they are posting because they know a lot about this forum. People will keep sending merits to the account as long as the account is posting helpful information.
This could actually be your way of determining ALTs and in my opinion you can't actually tell a newbie is an alt because they are a good poster you could only speculate. The reason I'm saying this is that there are true newbies here that are quality posters but may be ignored because people think they are alts .
Who tells you that ranked members disclosed their alt? No evidence. It is the only the ones that you see that you know.
What that is important is to avoid posting low quality posts and also avoid spamming.
Not all but some have like little mouse mentioned. Nevertheless the fact remains you can't tell all alts on this forum. I'm not actually against the fact that there are many alts on the forum because that's actually the truth.