Need aero advice on car top business sign

[Cd]

I plan to add a sign to the top of my car, but would like to know the possible aerodynamic drawbacks.
I plan to create a sign with as minimal frontal area as possible when seen from the front of the car.
( The sign will be no more than 1/4 " thick, and preferably much thinner.)
I'm concerned about vortex shedding, and would like advice on the ideal shape to reduce it.

Of course, I'm going to take a big hit when it comes to crosswind drag, but this is unavoidable.
Any ideas on making the crosswind drag less of a problem ?
( What about using fine mesh window screen and painting my logo onto that ? Nah...not visible enough.)

What I have in mind is sort of a huge mohawk 'if you will' ( did i use that saying right ? ), or a sort of 'spine extension' on top of the roof.

Lastly, what would you all recommend as a streamlined way to attach it to the car ?
( Simple, large 'L' brackets ? )

I have no worries about drilling into the car, or otherwise 'destroying' the cars looks .....it's a junker business car.
I only worry about it blowing off, and leaks - but think the leaks should be fine if I caulk up the areas where the holes would be.

I think my main frontal drag will come from any brackets and such that I use to keep the sign on the car.

I'll post some design sketches later, and do some sloppy CFD tests.
I'll let you all know what kind of drag hit I'm looking at.

[Frank Lee]

https://www.google.com/search?q=car+...gxBlsQ_AUIBygC

Some use luggage rack crossbars- no holes but not aero.

Some use magnets- no holes and good aero.

Re: x-wind: I was thinking of pivoting the panel from the front edge like a rudder, then perhaps limiting the movement to, say, 45 deg either side, and dampening the swing somehow- rubbery friction washers on the pivot mast and/or bungees or?

You need this:

[nemo]

Might consider rear windows for advertising.

[ksa8907]

Look to nature for the shape.

Shark fins or tuna fins.

[aerohead]

*I'm with nemo,use perforated graphics on the glass that you can see through,but looks 'solid' to an outside observer.
*Upper windshield might be available too
*as well as backlight

[ksa8907]

Could also do car wraps.

[cRiPpLe_rOoStEr]

Do something similar to an oversized shark-fin antenna and call it a day.

[Cd]

As far as a wrap, I don't have that kind of money.
I painted it by hand instead.
You can see it peeling off of the glass, but I just patch it up every now and then ( about once every 4-6 months.
And as far as the windows, all of them have advertising - except the ones I need to have clear for legal reasons.

Magnets ? I was just outside earlier and a gust of wind blew a branch out of a tree near me. I think I will be using bolts, or self tapping screws.

[botsapper]

Maybe the cleanest backlit 'wing' sign seen on the neighborhood pizza delivery cars.

HTH Inc. - Window Mounted Car Sign - Wing

[MobilOne]

Since you do pet portraits, why not a large dog or cat on the roof?

Or why not a portrait?