[andres]

What do you mean by filter icon?

[smokinn]

For filter icons usually a funnel is used:

http://images.google.ca/images?hl=en&source=hp&q=fil...

Magnifying glasses typically represent search.

[boucher]

I think the magnifying glass is perfectly acceptable here. I think the "filter" icon is much less recognizable to the majority of users. (case in point, the author of the app hasn't heard of it).

[Semiapies]

A funnel gives me precisely the opposite connotations as filtering.