Brackets that represent a filled tick-
box. Hence the writer is asserting that the statement following the brackets is true, or wants to highlight the presence of something or other.
{
x} is the opposite of { }, an unchecked tick-
box which means the statement is false or missing.
Multiple tick-boxes are often strung together,
like a
check-list of true and false statements.
(Note - curly brackets are used in the examples, since urbandictionary uses square brackets to denote links. However in real usage, square brackets should always be used.)