Don't forget to keep your eyes peeled for signs and special instructions like these:

Hiking Trail
Visitor Information
Trail or road where biking permitted
  Area where pets under physical control permitted
Place garbage here
Handicap-accessible facility
First-Aid Station or Hospital
Public overnight accommodations
Area where parking of motor vehicles permitted
Area where picnicking permitted
Restrooms for both men and women
   Tunnel
Swimming permitted
Area where public camping permitted
Interpretive Trail
Area where trailers or trailer camping permitted
Trailer Sanitary Station for dumping waste from holding tanks
   Area of Falling Rocks
   Fishing permitted

When the above symbols are displayed with a red slash superimposed over the symbol, this indicates the activity is prohibited.