In the introductory notes to a critical edition of Charpentier's Élévation au St Sacrement, C. Jane Gosine writes (emphasis added):
With no extant ornament tables by Charpentier, nor explanations of ornamentation,
interpreting Charpentier’s ornamentation remains somewhat conjectural. Charpentier uses two
ornament symbols in “O amantissime salvator noster Jesu dulcis”: the tremblement simple (which
is the most commonly found ornament symbol found in Charpentier’s autograph manuscripts)
and a tremblement symbol preceded by a dot. Although in many instances within the Meslanges
autographs, Charpentier writes out a termination for the tremblement (and this is even more
common where Charpentier uses the double tremblement sign), there are no such instances in this
motet. Evidence found elsewhere in the manuscript and comparisons with contemporary French
composers suggest that the tremblement was usually approached from above.
The second ornament appears to be similar to that used by D’Anglebert and described as a
tremblement appuyé––a tremblement with a preparation on the given main note. In some
instances elsewhere in the Meslanges autographes the dot is written over a half note tied to
another half note of the same pitch, over which is written the tremblement. In this motet the dot
and tremblement occur over long notes.... The evidence suggests therefore that the dot indicates the tremblement should begin with
the main note being held before the tremblement itself begins. The main written note therefore
becomes part of the ornament pattern––part of the trill itself.
I.e.: While most of these trills start from above, this one starts by sustaining the main note, and the trill comes toward the end of its duration.