s是什么类型的签证？
visa stamp on your passport -> visa， no other letters in the word. So this is a regular tourist visa (B1/B2) which you can enter with or without a prearranged tour plan. There are some more types of visas， but they all have different stamps： D for transit; C for work visa and so forth. But never ever "C1"， if it appears there somewhere its just some kind of mistake by immigration officer who didn't know how to write English. As well as I don't think that someone would use such an abbreviation for something like temporary visit visa， especcially when he knows perfectly good enlgish words for these purpose： B1 ，B2 etc. Also， please note that visas should be written both ways ： left to right 和right to left. If yours looks funny one was mistaken while issuing or scanning it into database； otherwise it will look completely wrong. For example： J5 instead of A5， E3 instead of T3， etc.
And about your second question： yes. It means that you came not under invitation of any company or person（as far as we see from your entry documents） ，and thus may face problems at airport customs upon arrival： they could deny letting you step off plane and out of terminal building even after boarding call has been made． That's because you did not present any papers proving that you were allowed to come here legally according their rules， so why should let you through？ In order to avoid difficulties and complications， try contacting your host before coming to Russia： tell him what document should he send to embassy where you get visa to prove that you arrived in accordance with his agreement terms （which， by the way does exist since visas are issued according to some agreement between Russia and certain foreign governments）or else ask for personal meeting in airport（not advisable though！）. You might also want to print out copies of email communication where you got approval letter from them along with original signed contract －that might help too. Remember always： Russian law enforcement officials must do everything legally，so anything illegal done by you will make things even worse than they actually need to be！ Good luck ：)