The di'teh was an aura given off by shrouded Jem'Hadar. The di'teh could only be detected by other Jem'Hadar, and only at close range.

In April of 2376 the Jem'Hadar Taran'atar used his ability to detect di'teh to track down and dispatch a number of shrouded Jem'Hadar who were attempting to destroy Deep Space 9. (DS9 novel: Avatar)

Ordinarily Jem'Hadar would not be working against each other and so the di'teh is presumably an ability given to the Jem'Hadar to allow units to continue to function as a team when shrouded.