It's not clear if you are looking for a death indicator that's just for you in using RM, or if you are looking for a death indicator that will appear in reports.
I think the question is trickier than it first sounds. I admit that I have a lot of people in my database who clearly are no longer living (for example, they were born in 1753) but for whom I don't have a Death fact because I don't know when they died. I think that an undated Death fact reads awkwardly in reports. I usually try to come up with a reasonable estimate for a death date if I can, but sometimes it's hard to come up with a reasonable date.
On the other hand, suppose someone was born in 1930 so that they might still be living, and suppose the were listed as deceased in a family member's obituary in 2003. In this case, I would probably enter a death fact for the person of "before 2003". And better yet in this case, since there is a good likelihood of being able to find the death date, I would probably invest the time to search the SSDI, findagrave, etc. to see if I could find a death date. Other situations might be where somebody appeared in the 1850 census as age 3 and were not enumerated in the 1860 census. In this case, I would probably enter a death fact of "between 1850 and 1860" or something like that. In this latter case, there's at least a chance that the person didn't die before 1860 and simply was somewhere else at the time of the census enumeration, so as I said originally it can be very tricky.