You can see the critical areas on the airport diagram:

http://www.naco.faa.gov/d-tpp/0513/00375AD.PDF
from
http://www.naco.faa.gov/index.asp?xml=naco/online/d_tpp

The areas near the bottom labelled "CAT 1 HOLD", "CAT 2 HOLD", "CAT 3 HOLD" are lines that the tower protects traffic from crossing during ILS operations of that catagory.

As you taxi for takeoff, you may see a sign that say "ILS". From the Aeronautical Information Manual ( http://www.faa.gov/atpubs/aim/ ):

Holding Position Markings for Instrument Landing System (ILS). Holding position markings for ILS/MLS critical areas consist of two yellow solid lines spaced two feet apart connected by pairs of solid lines spaced ten feet apart extending across the width of the taxiway as shown. (See FIG 2-3-16.) A sign with an inscription in white on a red background is installed adjacent to these hold position markings. When the ILS critical area is being protected, the pilot should stop so no part of the aircraft extends beyond the holding position marking. When approaching the holding position marking, a pilot should not cross the marking without ATC clearance. ILS critical area is not clear until all parts of the aircraft have crossed the applicable holding position marking.