I put the two characters in a txt file and did a hex dump

Hmm.

1. What program did you use to create the text file on the Windows machine?
2. How did you transfer the text file to the Linux machine?

ff fe b1 00 0d 00 0a 00 92 25

Allowing for the little-endian-ness of Windows (and Linux) reordering of bytes:

0xFFFE : magic number for UTF-8
0x00B1 : decimal 177 for ±
0x000D : decimal 13 for CR (carriage return)
0x000A : decimal 10 for LF (linefeed)
0x2592 : decimal 9618 for Medium Shade ▒

According to this page, you can get it in Windows by typing Alt-2592 or Alt-177. Go figure.

Ceci n'est pas un seing.