"Sorry, sign slowly, please". Familiar, eh? :)
How to sign "slow" in American Sign Language (ASL)?
Definition: Not fast; moving, flowing, or proceeding without speed or at less than usual speed.
Pronunciation/articulation: Dominant "5" hand (handshape), palm facing down (palm orientation) on the top of the passive hand (location) moves backward along the hand (movement).
Deaf signers infect this base word to convey nuances of meanings, such as "so slow!", "unbelievably slow" and such. Intonation (e.g. facial expression) is accompanied.
Ironically, the movement for one of the inflections is fast and short with intonation. But, that's the way it is.
"Sign slowly, please" or "Fingerspell again, please. Slow." Deaf signers have seen this phrase many times in everyday social or work life. Beginners use them sometimes or many times. Or, maybe some of them are afraid to ask a Deaf signer to be slow, pretending to understand, yeah? :)
In ASL classes, Deaf ASL instructors don't sign slowly, but rather use variable, controlled speeds, depending on the contexts and dynamics. E.g. introducing new vocabulary for the first time, using them again with increased speed in a session, an overall gradual speed over each semester, a degree of difficulty, etc.
In parallel, a learner is expected to increase their receptive skill by attending classes regularly, doing homework, and participating in group practices.
First 100 words.
As you feel more comfortable with the first few hundreds of ASL signs, progress further with your vocabulary and learn signing more.