Constraints and Business Rules
Strangely enough those projects that are usually most successful have to deal with a number of business defined constraints or explicit business rules. The lack of defined constraints and business rules is a clear indicator that the risk management may not be of sufficient maturity.
Is the project the master of its own destiny, or is it dependent on external factors out of its control? If it is the latter you can almost guaranteed failure.
Whilst these indicators are not absolute I have found that they give me good insight into whether a project has the potential to be successful. More importantly, they provide a means to clearly articulate the risks to the project. At least a defined risk can be managed.