Ammianus Marcellinus, Res Gestae 17.4, in the context of Constantius bringing an Egyptian obelisk to Rome, has a fair bit to say about hieroglyphs; whether any of it is accurate is beyond my knowledge, but it seems unlikely to me. He also includes a Greek translation of the hieroglyphs on an obelisk in the Circus Maximus, citing a certain Hermapion (otherwise unknown). Again, I can't say whether this is a reliable translation.
Here's the relevant part, with the Loeb translation:
Formarum autem innumeras notas, hieroglyphicas appellatas, quas ei undique videmus incisas, initialis sapientiae vetus insignivit auctoritas. 9 Volucrum enim ferarumque, etiam alieni mundi, genera multa sculpentes ad aevi quoque sequentis aetates ut inpetratorum vulgatius perveniret memoria, promissa vel soluta regum vota monstrabant. 10 Non enim ut nunc litterarum numerus praestitutus et facilis exprimit quicquid humana mens concipere potest, ita prisci quoque scriptitarunt Aegyptii, sed singulae litterae singulis nominibus serviebant et verbis; non numquam significabant integros sensus. 11 Cuius rei scientiam his inseram duobus exemplis. per vulturem naturae vocabulum pandunt, quia mares nullos posse inter has alites inveniri rationes memorant physicae, perque speciem apis mella conficientis indicant regem moderatori cum iucunditate aculeos quoque innasci debere his signis ostendentes. et similia plurima.
Now the infinite carvings of characters called hieroglyphics, which we see cut into it on every side, have been made known by an ancient authority of primeval wisdom.* 9. For by engraving many kinds of birds and beasts, even of another world, in order that the memory of their achievements might the more widely reach generations of a subsequent age, they registered the vows of kings, either promised or performed. 10. For not as nowadays, when a fixed and easy series of letters expresses whatever the mind of man may conceive, did the ancient Egyptians also write; but individual characters stood for individual nouns and verbs; and sometimes they meant whole phrases. 11. The principle of this thing for the time it will suffice to illustrate with these two examples: by a vulture they represent the word “nature,” because, as natural history records, no males can be found among these birds; and under the figure of a bee making honey they designate “a king,” showing by this imagery that in a ruler sweetness should be combined with a sting as well; and there are many similar instances.
*This is not how I took that phrase; to me it seems like "have been made famous/remarkable by the ancient authority of primeval wisdom," i.e. the fact that they're so old, and old things are thought to contain extra wisdom/authority, makes them particularly interesting to people.
 Tongue.gif "(1) Tongue out :p")
