Might be melting if you've been out in the rain
In the old days you'd have thought it could be an emulsion of water, rust and oil from a cable but these days (anytime in the last 20 years) they're usually lined so it's possible the linings worn through somewhere.
Can't think of anything else that's oily and reddish used in the motor, the only other thing would be rust oil water combo from the chain or even ACF50 which I think is reddish??