There are no widely accepted standard symbols for either median or range.
That said, it is somewhat common to use “m” to stand in for the median in various mathematical expressions (see first link below, for example).
Mathworld suggests that mu_(1/2) or x-tilde (see mathworld link for symbols) are common but I’ve never seen them used.
If X represents your dataset then range = max(X) – min(X). I don’t recall ever seeing any particular symbol for the range.
Mathworld, in their definition, use “R” for range but…
Symbol For Median
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What are the symbols for Range and Median? O_o?