You can use HamSandwich and hook AddPlayerItem. Not tested:
Code:
#include <amxmodx>
#include <fakemeta>
#include <hamsandwich>
public plugin_init()
RegisterHam(Ham_AddPlayerItem,"fwAddPlayerItem")
public fwAddPlayerItem(player,item)
{
static classname[32]
pev(item,pev_classname,classname,charsmax(classname))
if(equali(classname,"weapon_c4"))
client_print(player,print_center,"BOMB PICKUP EVENT")
return HAM_IGNORED
}