Anyone who has ever played with street chalk as a kid should know that the chalk become smeared or washed away when it rains.

In order for this to even work you need LOCATION, LOCATION, & LOCATION

Personally I think this isn't anything to worry about I mean if you do manage to get a signal your still going to need some time to setup & time on getting the dailup even if you manage to get some chalk and write down info about it and write about the signaling on some encripted chalk scribbleing so that you can come back later to that spot or have a friend check it out there is still the issue of standing around and waiting for it to work.