The only way to have it turn off completely when down is to use a PIG2. There's nothing in the game that turns on when the bank is up, and off when the bank is down already, and definitely not at the 12v needed to really make the mod pop.
How noticeable it is in "default" mode without a pig2 when it's down is kind of subjective. If you have a lot of bright LED GI, eli ramps, and overhead lighting (i.e. aren't playing in a dim room), then it's not going to be hardly noticeable at all that there's a light under there, except maybe around the edge of the bank itself. I have incandescent GI (and the Eli..) still in my game and even with the lighting in my place, I was gonna program my PIG2 to be WAY brighter when down because I want that illumination when it's down. If you're playing in the dark it would be more noticeable.
Alternatively, my only other idea is maybe you could always put a black strip under the decal itself, then put the decal on top of the strip if you just don't want that illumation at all while it's down, but don't have the PIG2. The decal as-is is only mildly translucent...the only place you can see any light at all coming through the decal is in the yellow traces, IMO. I expect it to be at ALL when I put it on there. That's why I've been bugging Brock for one printed on a transparent decal, lol. Differn't strokes and all that.
Again, kinda busy tonight, but when I get in there, I'll try and take some more pictures of it under various conditions...you can then decide for yourself or mod further from there. As I said before, only so much I can do on this, because I am not the one making the decals, and I don't feel like I have a better solution than what Brock made.. in a perfect world, I'd want to sell all three types of decals...the one he currently makes, a transparent one that allows a lot of light through, and a completely solid one, but I don't really have that option. =\