When I worked in the automotive electronics industry, we would have all of our IC's custom marked with our internal part number. No manufacturer information was allowed on the outside of the part except for a date code and lot code in our format. This added some cost to the parts, but it was not terribly expensive nor was it bulletproof.

 You need to ask your customer to what end they want to prevent rev. eng. on their products. The costs rise rapidly as you try to make them more secure. At best, you can keep the honest thieves honest.