Cameo is
usually only on proof coins. There is rare instances where a MS coin will have it (More common MS cameos come from the SMS sets from the late 60's).
If you have a PCGS MS-70 G.W. dollar, it's worth roughly, well, i don't know, no price guide has MS-70 references.
If you have a G.W. PF-70 DCAM dollar, it's worth considerably less due to the fact that PF-70 coins are a lot easier to find than MS-70.
If one had a G.W. dollar, MS-70 cameo or deep cameo, it would be worth a TON of money. Though, i have never seen nor heard of one, and none of us probably ever will.
Cameo is achieved by polishing the fields, and not the devices on a die, causing a contrast between "frosty and mirror".
Hope this helped, i just woke up 20 minutes ago and haven't gotten any coffee yet, So, it might be a bit hard to understand
