Something like this
https://cdn3.iconfinder.com/data/icons/map/500/wrong-512.png
The first one is more consistent with Google's labelled markers.
I don't know our current ones are to the side, like the second one.
Yeah, we should probably update those at some stage to match Google's (see add location and edit location, for example).
The extended set includes an icon called not listed location, which might be suitable here, too.

@PeterShaggyNoble good point.
I much prefer the modifier within the icon than to the side. If they were used on a map the small external icon could be easily lost in the maps details.
I agree I was just merely making a consistency point.
Added. 馃槂
Most helpful comment
The first one is more consistent with Google's labelled markers.