Formatting

JamesBurke  In the Overview Card 2 try the below.

Overview Card 2 =
VAR _Change = CALCULATE([Card 2 %])
RETURN
FORMAT(_Change, "Percent") & " " & IF(_Change > 0 , "▲", "▼")

JamesBurke ,
That's the default behaviour of Format DAX function when provided exact format. Here's what you can do apart from the solution BIstvan provided:

__Zero_Format_Test =
VAR _Change = 0.002002
Return
IF(
    _Change < 1,
    FORMAT(_Change, "0.## % "),
    FORMAT(_Change, "##.## % ")
)
& " " & IF(_Change > 0 , "▲", "▼")

Output: