Personally, I don't care at all about the signatures. But some do, like Russian notes printed between 1909 - 1910 have the rarest 'Timeshev' signature which increases the value by ALOT. Then ones printed between 1910 - 1912 have the more common but still rare 'Konshin' signature, they cost less than the 'Timeshevs' and then there is the notes printed between 1912 - 1917 which have the extremely common 'Shipov' signature. In UNC condition the 'Shipov' notes are worth only about $5.
I would think if your interested in buying just random notes, not trying to complete sets then just stick with the cheaper varieties.