So, I found the thread via google since I had the same question.
For those who will do the same, here is how MarkValue works:
MarkValue is a bit-field, which means that each mark has its own bit.
The marks in binary are as follows:
● 0000.0000.0001 (1)
● 0000.0000.0010 (2)
▲ 0000.0000.0100 (4)
▲ 0000.0000.1000 (8)
■ 0000.0001.0000 (16)
■ 0000.0010.0000 (32)
♥ 0000.0100.0000 (64)
♥ 0000.1000.0000 (128)
★ 0001.0000.0000 (256)
★ 0010.0000.0000 (512)
✦ 0100.0000.0000 (1024)
✦ 1000.0000.0000 (2048)
You can combine multiple markings by combining the bits, i.e.:
●▲■♥★✦ = 1010.1001.0110 (2710)
Obviously the red and blue mark with the same symbol are mutually exclusive, aka you should not set them at the same time.
In the batch editor you will have to use the decimal value, which I included in parentheses.
Example: Mark all shiny pokemon with ★:
=IsShiny=true
.MarkValue=512
You can use a binary to decimal converter to get the decimal value of combined marks.