Final answer:
The most reliable clinical sign of gingival inflammation is bleeding gums, which indicates disruption of the gingival tissues typically by microbial infection.
Step-by-step explanation:
The most reliable clinical sign of gingival inflammation is bleeding gums. The four cardinal signs of inflammation include redness, swelling, pain, and local heat, with a possible fifth sign being loss of function. Among these, bleeding is particularly indicative of gingival inflammation because it results from the disruption of the integrity of the gingival tissues, often by microbial infection, which is a hallmark of conditions such as gingivitis and periodontitis.
Other signs such as redness and swelling of the gums, bad breath, and receding gums can also be associated with gingival disease, but they may also be present in less inflamed states or could be due to other factors.