For FM repeaters, many of us used our own calls. That's not a suggested solution for D-STAR. A Repeater System's call sign should not be the same as any user's call sign.
In the US, this means that a club station call sign will have to be acquired. If your club already has a repeater call sign, this would be an excellent choice. But if the club expects to use the call sign as a end station, as in a communications van or even field day, then an additional call sign should be acquired.
The FCC allows clubs to request as many call signs as desired. It only takes a few days to get a new call sign. But if your organization, as many do, wants a vanity call sign for their D-STAR System, then the FCC requires a significant wait period. Therefore it is imperative that the call sign process should be started as soon as possible so that the vanity delay will not cause too much of an issue.
D-STAR call signs are limited to no longer than 6 characters. This shouldn't impact any locations, but there are some localities that are now issuing 7 character call signs. I do not believe that these are licensed for repeater ownership at this time, so it isn't a problem.
While short call signs are often advantageous, when programming a D-STAR radio, 6 character call signs are often easier to program. Any unused character positions must be filled by a space, and since spaces are normally invisible, it can be hard to see if the correct number of spaces have been used.