Není doporučeno, ale můžete zkusit toto:
dollar = "\uFF04";
$
dot = "\uFF0E"
.
db.test.save({[dollar]:dot})
WriteResult({ "nInserted" : 1 })
db.test.save({[dot]:dollar})
WriteResult({ "nInserted" : 1 })
db.test.find()
{ "_id" : ObjectId("58256b0f9934a5d1c696c456"), "$" : "." }
{ "_id" : ObjectId("58256d359934a5d1c696c457"), "." : "$" }