Unfortunately, a line is missing, but this is part of a poem that some lonely prisoner wrote probably to remind him of his wife or girlfriend back home. This is a freehand translation, so it has lost a little something in the process!

Lieb, so Lang Du Lieben kannst - Dear, so long your love knows
Lieb, so Lang Du Lieben magst - Dear, so long your love likes
Es kommt die Zeit, er kommt die Tag - It comes the time comes, it comes the day

The last missing line reads: "Wo Du an Gräbern stehst und klagst" It is a poem written by Ferdinand von Freiligrath, 1810-1876, and the prisoner has changed certain words.