The whole point of raising Sepsis awareness is that it isn't obvious and when it is obvious it's often too late.
Read the story of Tom Ray. A tiny nick in his mouth from a visit to a dental surgery, coupled with a chest infection. He had stomach pain and thought he had food poisoning. He now has no lower arms, no lower legs, and half his face missing.
We have the FAST campaign for stroke. Face, Arms, Speech, Time. Many people who fail the FAST test won't have had a stroke, but it will save lives if the ones who have are caught.
Meningitis - people know about stiff necks, aversion to light and rashes.
This is no different. Sudden confusion, high heart rate, high or low temperature, breathlessness, pain out of character for the injury.
The basic rule should be 'it's sepsis until it isn't' because treating for sepsis does no harm and missing sepsis leads to death or life changing injury.