Its impossible to tell the difference between (1) a friendly mine (or friendly bubble...etc.); or (2) Enemy mine/bubble/etc.
These things should have different colours: i.e. Alpha team is RED, Other team is Green.
EDIT: Don't forget thaose electric mines which are hardly hidden... just of unknown threat level (friendly/enemy)
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Yesterday i sought refuge in an empty bubble I thought was a teammates'. I went blind.