I would say it really depends where you are taking those pictures:

In SFO, nobody bothers me when I was taking pictures in front of Bayfront Park & The Fishing Area (or Fishing "Pier") next to Coyote Point:

http://flygga.tripod.com/SFO.html

However, I was busted & ticketed once by the airport police while I was shooting in front of the fence for the QANTAS at the ramp at South McDonnell Road.

In LAX, no one cares if you are at the Imperial Hill, In-n-Out Burger, Proud Bird Restaurant, & Flight Path Learning Center.

http://www.spotterswiki.com/index.php?title=LAX

Nevertheless, I was being question by airport police & ask me to go (no photo) such as places like the 96th Street Bridge (the bridge over pass South Sepulveda Blvd, part of the Pacific Coast Highway) & the roof top of the "Parking Spot" next to In & Out Burger.

In NRT, no problem on the observation deck at Terminal 2 & Sakura no Yama Park:

http://www2s.biglobe.ne.jp/~ito-nori/spot/spot_nrt1.htm

But if you are on the observation deck at Terminal 1, the patrol policemen will keep bothering you in every 30 mins.

In SIN, no problem at Terminal 1, 2, & 3 Public Indoor Viewing Malls.

http://www.spotterswiki.com/index.ph...ort_(SIN/WSSS)

But if you shooting at Changi Beach Park, Changi Business Park, & Changi Coast Road you may be questions by the local authority & ask you to go as well.