What are these symbols in nginx error.log?

Question

Nginx

Strange sequences come to error.log. Example below, the first two lines are normal, the other two are the same. What is this nonsense? Should I be afraid?

66.249.81.174 - - [23/Mar/2014:23:04:34 +0400] "GET / HTTP/1.1" 200 612 "-" "Mozilla/5.0 (Windows NT 6.1; rv:6.0) Gecko/20110814 Firefox/6.0 Google favicon"
66.249.81.174 - - [23/Mar/2014:23:04:34 +0400] "GET /favicon.ico HTTP/1.1" 404 169 "-" "Mozilla/5.0 (Windows NT 6.1; rv:6.0) Gecko/20110814 Firefox/6.0 Google favicon"
83.149.9.191 - - [23/Mar/2014:23:05:40 +0400] "\x94\xED\x80\xA5\xC8g\xF1\xA7\xDBc\xCB\xAEjR\x22\xF6\xA1&e\xF5\x97\xB3\xC0\xC2\xD3%\x0EE\xC8g\xD5\xF5\x98\xBBP\xF1px\xB5\xC7\x5C\xA5\xF09\x02\xE6\x8Cl\xEC:\xA7;\xC3Z\x7F\xD1\x9FR\x8B\xBB\x04\x8DmI7\xFB\xB4" 400 173 "-" "-"
31.180.122.64 - - [23/Mar/2014:23:08:36 +0400] "\xF2\x1B\x97\xE1\x22O\x1E\xFF&x\xA5\xDB`\xF3k\xD2\x22\x82\xAC\x8A\xAD\x02V_%a\x96\xE4\x04T\x9FxQ\x8E\xDF\xCF\xA5nl\x7FE\x8A'\xCA\xEB\x1AZ\x91\xFE\xB5^>\x1D" 400 173 "-" "-"

Answer 1

Someone is feeling tricky requests. For exploits etc.