First the emblems must be cleaned of any dirt , grease or paint chips if any. Use paint remover , fine sandpaper or whatever is needed . Then wash and rinse the thoroughly with soap and water and allow the clean emblem to dry.
Once dry , you then prime the emblem with a self etching primer using 2 or 3 coats and allow to dry as recommended on the primer's application instructions. . Using the Self Etching Prinmer is very important for long lasting adhesion to the aluminum surfaces.
Now you will paint the primed emblem with whatever paint you decide to use and allow to dry as directed on the insturctions. You can the entire front surface including the lettering which will be covered later.
Once the paint is dry you will set up a "sanding block" with a fine sandpaper of maybe #300 grit or finer if you like. Secure this to a bench or table so you wont have to hold it. Sandpaper side up!
Then turn the emblem face down and rub it on the sandpaper to "scrape" the paint off of the raised lettering surface. Be careful to apply even pressure and observe the emblem face often to monitor progress and adjust your pressure points as needed. Continue until the lettering is as clean as you would like it. You can now use a finer sandpaper if wish to remove any scratches , or leave as is .
Finally , if you wish you can clear coat the emblem or leave as is. You may have to buff the exposed aluminum lettering after some time if you like them to shine like the sun.

This has worked for me and is a fairly straight forward and quick process with good results..