activists installed snowden 's bust on top of century-old prison ship martyrs monument at fort greene park before dawn monday .
it took them six months to create the 4-foot-high , 100-pound bust sculpted out of plaster-like material and made to look like bronze .
bust was accompanied by block letters spelling out ` snowden '
less than 10 hours after installation , parks workers swooped in and took down the statue .
the unsanctioned bust appeared in the park just hours after hbo aired john oliver 's interview with edward snowden .