How to place an indicator light for 24 VDC Solenoid Valve?
There is no such thing as a "24 V LED".  However, you can use a resistor in series with a LED so that the combination can be safely lit from 24 V.  Let's say you want 5 mA thru the LED, and that the LED drops 2.1 V (typical of normal green LEDs).  From Ohm's law, (24V - 2.1V) / 5 mA = 4.4 k&Omega;, which is roughly a suitable resistance.

Keep the power dissipation in mind.  The resistor will drop about 22 V, which times 5 mA is 110 mW.  That's getting close to the limit of a "1/8 W" resistor, so either make sure a 1/8 W resistor is properly mounted at the right temperature or use a 1/2 W resistor.  Note that the power dissipation in the resitor is proportional to the LED current, which is one consideration for keeping the current low.