I have noticed the certain posts are surrounded my a rectangular shape on the right hand side while others are not.
Please explain the significance or non significance of the rectangle.
The discussion entitle '95 doorlock & alarm is one example.
I have attached a screenshot for your review.
Thank you.

Certain discussions display rectangles while others do not.

 

.... is the only one that hasn't had a new post added since your last visit/update. All the others have posts you have yet to read. Is my guess...

 

^^ nailed it.