It is one of the ASCII art
"キタ━━━━(゜∀゜)━━━━!"An abbreviated form of
The expression that something emphasizes an appearance / an appearance/surprise/expectation when it occurred.
An origin
In a commercial of "サンテ FX" of the first half of 90's, Yuji Oda places eyewash and depends on having exclaimed with "キターーー".
2ch ー nera used it willingly
Even the public seems to use it recently.
"Desu" does not mean period. It can be used kind of like "is" (the verb "to be"). But, I think, more correctly it is a coupula which is a grammatical thing of it's own.
"ka" 「か」 can be thought of as a question mark, but really it's a particle, not a punctuation. "no" 「の」 can also be used to make a sentence a question.