Leaving a blood trail
Break out the bloodhound Splicers!

I feel this also ties into the suggestion there was for more ambient blood splatter in general, such as some chummer in the crowd getting covered in blood during fights. I could 100% go for blood trails standing out if someone's legitimately bleeding out all over the place. Maybe having varying degrees of obviousness and age, with factors like weather and light conditions affecting the visibility (Is it dark, therefore harder to see a dark red on dark concrete in this dark alley, is it raining, therefore diluting and washing away the blood spatters?)

To add to this, having blood spatter cover walls and stuff after recent and particularly bloody battles and firefights could also be incredibly cool.