What does 시참 mean?
I usually see '시참' attached to a name of a game, for example:

PUBG시참
Overwatch시참

But I can't figure out what does that word mean??

Question

What does 시참 mean?
I usually see '시참' attached to a name of a game, for example:

PUBG시참
Overwatch시참

But I can't figure out what does that word mean??

Answer

@Edjerha Oh! I see, thank you much! ^^

Answer

반갑습니다~!

'시참' is frequently used in game streaming and an abbreviation of '시청자 참여 (viewer participation)'. 
In the examples you gave, the game rooms are live streamed with viewer participation.