BLACK RECTANGULAR BOX ON TV SCREEN

Curiosity May Have Killed the Cat BUT Satisfaction Brought It Back!!!

PLEASE bear with the long and drawn-out specifics of my situation below as there was no plausible answer found in the many replies submitted for the often-asked 'black box' question:

1) My TV uses a digital antenna as opposed to any cable or dish;
2) My CC is turned off;
3) Many, many months ago, momentarily blocking the mid-to-lower portion of my TV screen, a centered medium-sized blank black rectangular box quickly flashed on then off;
4) The black box immediately flashed on and off again several times but this time each box showed white text as if my digital antenna was picking up on some unknown parties' private back-n-forth texting conversation;
5) With the conversation apparently ended after a minute or so, the black box has made no other appearances since those many months ago;
6) That is until TODAY's (09/04/2015) eerie incident!!!
7) At about 7:30am PST, my girlfriend was watching TV when that blank black box flashed on/off, then on again but this time instead of showing the conversing text of who-knows-who the white text read "lb's jt teasing you!" and nothing more, black box flashed off and was gone!
6) Here's the eerie part: My girlfriend's Mother's initials are 'lb' (with whom she was very, very close) and the one-year anniversary of her Mother's passing is fast approaching.
7) Now my girlfriend's not superstitious to any degree but this does have her freaked out!
8) Coincidental? Over-active imagination? Other worldly?

BOTTOM LINE: Does any body out there know what exactly is the root of that black box?

Thanks for taking the time to read.