I know it just because I deal with a lot of spam in my day job and looking at the patterns of the sign up, it’s clear to me that’s what this is.
In my case a lot of the addresses are .ru and the screen names are a name followed by three letters and it the email address itself is gibberish.
And example for screen name would be Steveheb and the email would be like [email protected]. That combo makes no sense to start and to see that pattern over and over, it’s clearly spam.
