JetS3t properties (user defined properties) are ignored when <useSignature> is set to true. Read on for more details.
When <useSignature> is set to true, Artifactory initializes an additional RestS3Service and uses it to send signed requests to AWS (exists, add, get, delete all use this object). The problem is that we're not initializing it properly and the custom props that should be injected using the binarystore.xml are only preserved with one of the RestS3Service objects (not the one that's used to send signed requests).
This has implications on various things such as SSE (server side encryption), which can't be used when using signed requests, and other properties which aren't effective (such as s3 connection pool size, etc)