Final answer:
Brake fluid is not included in the signature service because it is part of a closed system that does not require frequent top-offs or changes.
Step-by-step explanation:
The reason brake fluid is not typically added as part of a signature service at many auto service centers is that it does not usually need to be topped off or changed as often as other fluids in your vehicle. Signature service generally includes oil changes, checking tire pressure, and replenishing windshield wiper fluid. Brake fluid, however, is part of a closed system and should only be added or changed if there are signs of leakage, or contamination, or during routine brake service, which is less frequent than the services covered under signature service.
When brake fluid levels are low, it could indicate a leak or that the brake pads are worn down and need replacement, which are issues that would be addressed through a more comprehensive brake system service rather than a basic maintenance package. Vehicle safety needs to maintain proper brake fluid levels and quality, so when it is time to service the brakes or if an issue is suspected, it's important to visit a mechanic who can properly assess and perform the necessary actions.