Hi. You can set the Raster effects settings to 150 ppi, that setting only applies if you use raster effects like drop shadows. Ask your client which format he needs to receive the file, maybe the .ai file is ok. Don't worry about resolutions, ask your client the sizes he needs for the sign, sometimes is necessary just one size (1x or 100%), sometimes necessary different sizes like 1x and 2x, etc. If your sign has just vectors you can create your artboard to 1x and export it to any size. If you use images in your sign, you can create the artboard at a bigger size like 2x, which gives more image information for export to 2x, for example.
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