> Can you explain it one more time?

There is no one, universal sign language.

For example, there is Australian Sign Language (Auslan), American Sign Language (ASL), etc. They're all different languages.

I mean all spoken languages are just sounds, right? Sounds like one language to me, with multiple local dialects?

No, the type of sounds can be grouped into distinct language families and further down into language "branches". I just don't see (no pun intended) how this translates into different sign languages.

Any time you get enough deaf people in one place, who don't already have a signed language, they invent one. In times and places where signed languages have been suppressed, they've popped up all over the place at schools for the deaf. There's not much reason for any of the languages to share grammar and such with each other, since they're effectively unrelated. You wouldn't expect Japanese and Navaho to use similar grammar or vocabulary, right? Same here.

[Not Deaf, but I studied ASL and deaf culture for a few years at 2 colleges and in private lessons.]

There certainly are relationships between sign languages; A(merican)SL and French SL are arguably two dialects of the same language, or at least they were in relatively recent memory. Others are distantly related or unrelated; B(ritish)SL is absolutely unintelligible to signers of ASL and arose separately, for instance. Many of the modern global sign languages are related to one or the other of those families (and might be "dialects" as you want to call them, or might be further apart and thus merely "related languages"), but there are a few others that are not, including one—Nicaraguan Sign Language—that arose from scratch less than 40 years ago.

I think more comparable examples might be:

The symbol for 1 in different orthographies, such as: 1 I ١ ― 𒐕 一 etc ...

The words for father/mother are often a bilabial and open syllable combination regardless of language family origin.

The point is that while the details of the languages (sign, oral, written) could be different, there are some human affinities that make provide commonality. Another meta-pattern might that common words in many languages are often monosyllabic, though this is less universal than the two examples I gave above AFAIK.