Had the red bulb in my #153 signal go out, so, on the way home, I swung by the local auto parts store. I picked up a two-pack of #53 bulbs, dipped one in red Testor’s enamel, allowed to dry overnight and now the signal works fine! In fact, the OEM bulb I pulled from the signal is marked ‘53’, so you know where Lionel got 'em… 
These bulbs also work in 1122 switches and the like, so if you’ve got a dim bulb somewhere, hie thee off to Pep Boys or AutoZone or O’Reilly’s or NAPA or, well, you get the idea! 
VTY,
MMM
They are expensive purchased this way… you can buy them already painted(or clear) for .25 - .50 each HERE.
Rob
Those with 153 signals made before 1950, which have a 40-ohm resistor in series with the common terminal, will need number 50 lamps. If you want to remove the resistor, you can use either the number 1449, which is the same electrically as the number 363, or the number 52, which is similar electrically to the number 53 used in later 153 signals. Radio Shack carries the 50, 52, and 53. Here are all the lamp specifications:
50 miniature screw base, 7.5 volts, 220 milliamperes, 1000 hours
52 miniature screw base, 14.4 volts, 100 milliamperes, 1000 hours
1449 miniature screw base, 14 volts, 200 milliamperes, 250 hours
363 miniature bayonet base, 14 volts, 200 milliamperes, 250 hours
53 miniature-bayonet-base, 14.4 volts, 120 milliamperes, 1000 hours
Yus, but once you factor in a) $7.95 shipping and b) whatever shipping time happens to be, dropping in at the handy auto store makes sense. 
MMM
And, as a bonus, they’re a bit less expensive at RS (unless you know a mechanic, like I do, and can get a discount)… 
MMM