Escape every character in bash
This works for me with bsd sed-

echo "I am a jelly donut" | sed 's/./\\&amp;/g'
\I\ \a\m\ \a\ \j\e\l\l\y\ \d\o\n\u\t


and with your string

echo 'Example string 59^!#&amp;$(' | sed 's/./\\&amp;/g'
\E\x\a\m\p\l\e\ \s\t\r\i\n\g\ \5\9\^\!\#\&amp;\$\(