Above a door on the Royal Palace in Monte Carlo there is a version of the Arms, as shown above, with a Helm above the Crown and a Crest which would seem to be blazonned as follows:
Out of an open Crown (presumably or) a branch of Palm Leaves bendwise and a branch of Olive bendwise sinister (both either vert or proper).
However, this appears to come from the seal of the reigning Prince and is featured on the medal of a knight of the Order of Gramaldi, on stamps and on coins.