How to spot a copter
You can identify most DC area helicopters by looking at 3 features:
1. Number of blades - "how do see I that while it's moving," you ask? Take a photo!
2. What type of landing gear, skids or wheels? If wheels, how many are in the front relative to the back? Some helicopters have retractable landing gear as noted below
3. Lastly you can look at the shape of the tail, whether it strictly sweeps up, has a downward fin, or the tail rotor is enclosed in a fin.