MC is Member of Congress, also, USS is U.S. Senate or U.S. Senator, VP is Vice President, etc. The printed facsimile signature is their "free frank" to send mails.
Cut-outs like this have little value, but can be interesting.
To paint with a very broad brush, some entire envelopes from the more famous members have some value and the (let's say) pre-1900 ones are often actual signatures which command prices based on the autograph market.
Here are some "entires" in a thread I did several years ago:http://goscf.com/t/51608
Biographies of all these can be found in the printed "Biographical Directory of the United States Congress, 1774-" or through the on-line version:https://bioguide.congress.gov/