That's the kanji for "grass, weeds, herbs, etc." but knowing Sazanami, it's probably some 2chan meme or something like that. But if it were marijuana I'd expect 大麻 or 葉っぱ. So I'm not entirely sure how to translate this without the appropriate context.
To be precise, 笑う /warau/ (to laugh/smile) > 笑 (single character) > w (first letter) > wwwwwwwwwww (laughing a lot) > "hey, that looks like a field of grass, kinda" > 草 /kusa/ (grass). It also has a minor link to /kusukusu/ (the kinda quiet, behind-the-hand laughter).
It also led to 草不可避 (inevitable grass), meaning 'this will cause mirth without fail'; and 草生えた (grew grass) to mean 'that made me laugh'.
Pretty much, anything that can be used with grass (growing, cutting etc) can be used as a shorthand for a similar effect on laughter.
