If you see something, say something!
Here is a list of gas watching tips (pdf) from un-naturalgas.org.
U.S. Environmental Protection Agency's "Eyes on Drilling" tipline for non-emergency suspicious activity related to oil and natural gas development. Reports can be made by calling 1-877-919-4EPA or emailing eyesondrilling@epa.gov.
If possible, reports should include the location, time, and date of the suspicious activity, as well as the materials, equipment and vehicles involved and any observable environmental impacts.