http://live19.2ch.net/test/read.cgi/ogame/1151492937/l50
Hoofprint's not always up.
Some say it's up after certain moons, but hasn't been proven.
Some say it's a bug = appears 48 hours after maintenance only - which is when I found my, couple maintenances ago.
I'll keep an eye on the above link and let you know when they find one for Shiva :)