specific names of the siglum used on SH

[-JKP-]

There are some examples in German, in several dialects.

In one, it is a (ü) rather than a (v').  " v'ber / über ".  over

Yes, sometimes they wrote the umlaut as a cap (similar to VMS), or sometimes a small shape that looked like "c" (usually superscripted) but which we would now sometimes substitute as "e" (not superscripted) if it's a keyboard without an umlaut symbol. I have a few examples of those, but they tend to be older. By the 15th century, they were either leaving it out, or starting to write it as we do in modern script.

Some scribes used two symbols, one for the ü sound, the other (often a small "o") for an "oo" sound, like these:

   

Here's one that combines the two dots into a cap:

   

When I see it written like a small "c" shape (occasionally a small "e" shape), it's usually earlier than 15th century, but here is one from the 15th century: