What is "cigarette burn" a sign of in medicine?

S. Sharma; The ‘cigarette burn’ sign. QJM 2015; 108 (4): 347. doi: 10.1093/qjmed/hcu209

Cigarette burn mark: hidden clue

The eschar resembling ‘cigarette burn mark’ is seen in 95% of cases and is most important diagnostic clue of scrub typhus.4 It often goes unnoticed by both the physician and patient. Patients are often unaware of this mark as it is painless and non-itching. Early diagnosis by carefully examining the patient and prompt treatment is necessary as delay in treatment can result in life-threatening complications.