At the beginning of a stealth scenario, create a pool of Stealth Tokens for the PCs. Each Craft card has listed on it the number of Stealth Tokens it contributes to this pool. Crafts have a certain number of general Stealth Tokens, which are always contributed, and setting-specific Stealth Tokens that are only contributed in the proper setting. Stealth Tokens are combined into a single pool; they are not distinct for each PC.
Seekers and some other Challenges function by causing the PCs to lose Stealth Tokens instead of or in addition to EP. If the PCs lose their last Stealth Token, the scenario ends in failure as the PCs are discovered.
For more information, see Player's Guide Chapter 5: Exploration.