Not Many Tv Shows contain this much mystery and hidden details as The Big Bang Theory Cast. It has many elements in its Background Blurred by the Camera making it harder for the viewer to pay attention to them.
I uncovered 7 of them that I think most fans may fail to notice, and you might also like to know them or remind you of them.
7. Sheldon’s YouTube Account Name:
Many people have focused on the video that Sheldon was watching, when he was all drunk and making silly jokes on the stage in the presence of high profiles, to the point where he starts stripping down and showing his private spots to the audience.

If you take a look to the right side of the screen, you will notice a 3 letter word: “Ob1“, which is the same as Sheldon’s Jedi Master Hero, Obi-wan Kenobi, also called (Ob1 Kenobi).
6. Penny’s Fridge:
If you are like most people or a first time watcher of the show, you might think that the fridge in penny’s place has a typical random photos like other tv show do, unfortunately, you will be wrong.

Because if we zoom-in on them you will see photos of the actress Kaley Cuoco (the one who played Penny) during the big bang theory behind the scenes, and also some from her Private life.
5. Blossom References:
During the show, you might have heard for at least several about Blossom, because it has been used a lot by the cast members. Either when Sheldon was classifying the ideas that he and Amy come up with for Halloween costumes on his board, that’s when Amy bring up the possibility of using Blossom as a reference for their next Halloween costumes. Or when Sheldon was kicked out of the Physics ball team, the nerd boys were thinking about replacing him, that’s when raj bring up the Blossom girl.

If you were born in the 2000s it’s unlikely that you have seen Blossom. Blossom is a show from Disney-ABC Domestic Television Created in 1991-95, and happened to be one of Mayim Bialik’s (Amy Farrah Fowler) First Shows way before Joining the Big Bang Theory.
4. Apartment Numbers:
It is hard to pay attention to the door number while focusing on the story, especially when it was important unless you decided to re-watch the entire episode or the scene.

First, there is 314, Amy’s Apartment. Second, Wit Wilson’s Apartment, (a Star Trek Actor), its number is 1701, which is the exact registry number that belongs to the Star Trek Enterprise “the next generation”.
Last, 4A or pronounce “FORAY”, This Number is more about how it sounds not the number/letter. It is special because if you search for the meaning of FORAY in the Oxford dictionary, or just use google you will find that it means a Sudden Attack into Enemy Territory, Especially to Obtain Something.
3. Leonard’s and Sheldon’s Apartment Flag:
Which has a Gold Lion rampant on the field of azure, according to how Sheldon describes it in a Flashback episode. The Flag’s purpose as Sheldon put it, is to represent the state of distress in the apartment, it was turned upside down.

Example: When Leonard was playing or experimenting with chemicals, Sheldon comes in and warned Leonard about his mistake in the formula that he created, then Sheldon go and turned the flag upside down signaling the distressed state in the apartment due to the possibility of an explosion, which afterward he goes save Leonard’s life at the cost of blowing up the Elevator.
2. Sheldon’s T-Shirt Colors:
Like the flag, Sheldon decided to show his state of mind without talking, so he pick the color of his T-Shirts to be the indicator of his emotional state, kind of street lights or Codes.


Examples:
- The red T-Shirt means that Sheldon is angry and distressed.
- The green T-Shirt means that he is feeling brave.
- The yellow T-Shirt means that he is showing fear.
- The purple T-Shirt means that he is happy or showing affection.
- The Blue Ones represent Hope.
- and the Orange represents Greed.
1. The Appearance of Howard’s Mom:
In the Background, when Raj visited Howard’s Home then right when he was about to leave he was talking to Howard’s mom, that’s when she showed up in the background walking in the kitchen. for this one I think the video below will explain it better:

These are Just Few facts and details that real fans might enjoy or interested in, if you are Curious if there is more, there is another post about hidden facts from the Big Bang Theory. I think It Should be as much interesting.