So what does it really say?

There is no destruction (or damage).
There is no graffiti.
Let us enjoy/appreciate.

don’t break things
don’t paint graffiti
let us enjoy

Can mei2 you3 really be used as an imperative?

It makes more sense to me with the unstated filler as follows:

(IF) there is no destruction
(AND IF) there is no graffiti
(THEN THIS) lets us enjoy (THE ZOO).

I.e.,
A zoo without destruction and graffiti
is a zoo we can all enjoy and appreciate.

Thanks guys. I nearly managed the first one, but the other two were incomprehensible. This raises an issue I have with Chinese, which is determining subjunctives and imperatives. Aside from 要 being used for imperatives (sometimes?), what are some good guides?

DB, I’ve just seen your latest. You’ve identified my problem.

Edit: Oh, they meant scribbling (graffiti), not scrabbling.

Well, a bare verb or verbal phrase is imperative, like “Ting2 xia4 lai2!” 停下來! stop! (moving) or “Zhu4 shou3!” 住手! stop! (stay thine hand!).

You can add bu2yao4 不要 or its contraction bie2 別 or the written 勿 wu4 or more literary cognate 毋 wu2 (not to be confused with 無 wu2, meaning 沒有, there is no) in front of a verb for the negative imperative.

In many cases, context is the only guide; even then there can be some ambiguity.

沒有破壞
沒有塗鴉
讓我們欣賞

Other possible translations:

No vandalism and no graffiti makes things more enjoyable for us.
No vandalism and no graffiti affords us enjoyment.
Without vandalism or graffiti, we can better appreciate [the zoo].

Thanks for the help guys, especially that very useful detail DB.

Now, what’s the meaning of “Let us ZOO in?” Is this correct English?

Only when read in a mirror.

No, but it’s correct Chinglish!

Here’s my thesis:

IN = ENJOY; similar initial sound
ZOO = 人多聚集的地方 (place where many people gather) according to the Yahoo dictionary

Thus, “LET US ZOO IN” = Let’s enjoy this place where many people gather. :discodance: