Yes.
The only exception is if you have another Sigil in your mainhand that involves stacks on kill (For example, http://wiki.guildwars2.com/wiki/Sigil_of_Luck )
In that case, only the sigil in the mainhand would proc.
If you stack two sigils of blood, BOTH of them proc, but the cap is still 25. You just charge twice as fast.
