EF_ITEM_BLINK
From Valve Developer Community
EF_ITEM_BLINK is defined as 0x100, or 256.
This effect was added to Source as a supplement to items on Xbox.
This effects makes an entity have a flashing effect, so that it might be noticed easier.
Usage
To use this effect, turn off SmartEdit mode and add the following keyvalue pair to the entity: effects 256.
Note:If it is desired to use this with other effects, you should add the integer value of each effect to the value.Remember that you can set the effects value during runtime using an entity's AddOutput input with the input value effects x (x being any summation of effects flags to enable).
Warning:Using the AddOutput functionality for this, the new value may interfere with an entity's simulation functionality.