By definition, a milestone is a single event so, no, you cannot create a
single milestone with multiple dates.
On the other hand ... if you are adamant that you want something graphically
representing this situation then try this:
1. Create a task with 1 hr work and a duration of 4 days (one day for each
quarter; or a duration of 12 days if you're referring to months).
2. RightMouseButton on the task and choose "split task"
3. Position your mousepointer one day into the task, press and hold the
leftmousebutton and drag the task out to the first "milestone date". This
will leave a task marker on the first date and a dotted line joining it to
the remaining duration of the task. Repeat until you have a full set of
"milestones".
I don't like it; I recommend against it but you can graphically represent
your situation this way. And before you ask, no, there's no easy way to
replace those segments with diamonds.
JLB, PMP