Red triangle sign

[Txkun]

Yesterday, I was asked a question about a sign that can be seen in many windows of Tokyo buildings.
Since searching on the web gave no result and this seems an interesting thing to know, I want to share this picture with you.
So... what's the purpose / meaning of that red triangle?
I think Cocosan can help us!

Thanks!

[zengargoyle]

your google-fu is lacking. the triangles are for the fire department and mean that the window can be opened from the outside. (or easily broken)

see here in the section on Fire.

[coco]

Yes I've fixed the answer. ( made phone call and asked fire department)
zengargoyle-san 's is correct.
But they can not say easy to break, so they say "easy to enter ( ppl must not place stuff near the window with ▼ , etc .)" .
I think not so many Japanese know what is the purpose of it. 　( I didn't know what exactly is. :p)
Anyway good to know, Thanks Txkun.

[pikctsach]

souka, omoshiroi ne, hajimete sonna koto ga kiita (初めてそんなことが聞いた）

[colind]

Haha yeh... I asked a few Japanese people before I found that answer. A lot just don't know the real reason those red arrows are there. But its nice to know this little bit of information about Japanase buildings.

[Txkun]

I realized that I didn't thank you all for the interesting information (and I was told that I have this bad habit).
I'm sorry about that.
So...
THANKS!