How do you know you got picked in the lottery?

To the ones who updated their status to “Picked in lottery”: how do you know so early? Did you check if your check was cashed or something like that? Please comment. Thank you.

Once the petition is picked in the lottery, USCIS generates a receipt number for the petition. The receipt number is sent to the attorney or employer via email if Premium Processing or in regular mail for regular processing.

PS - not a legal advice.