By "mechanics" I meant more how the three interact with each other.
Street Cred is listed in the book both as increasing dice pools (p. 140) or social limit (p. 368) depending on where you look, for one. Street Cred is calculated as a known quantity and as a missions reward, true, but it can rack up some significant bonuses somewhat easily which seems at odds with Missions in general. For example, if you earn one street cred and 5 Karma per mission, that's +9 dice pool and/or social limit after just six missions. Guidelines on when Street Cred applies would also be good, as not everyone is going to know you're a stone cold professional, after all.
Notoriety is calculated manually but only for qualities in the core book and not any of the expanded (and Missions Legal) rules. This should be expanded upon. Notoriety also does not offset Street Cred in any way currently, so rules for that would be good. Some NPCs might even view Notoriety as a plus, which could be an interesting twist on the Cold Hearted Bastard rules re karma rewards, and/or could be used to influence intimidation rolls for example. Right now, however, it doesn't have much of a use.
Public Awareness is in the same boat as Notoriety. What exactly does it mean if your Public Awareness is 5? Does NPCs recognize you? Does it influence Street Cred and/or Notoriety, or vice versa?
In short, reputation is one of those very gray areas that would be difficult to effectively use in Missions because there's very little common ground for disparate GMs to use, and some outstanding rules clarifications that are needed.