By default ASA does not decrease the TTL field, hence is not visible in traceroute output. This is how to change this behaviour :
asa# conf t asa(config)# icmp unreachable rate-limit 10 burst-size 5 asa(config)# policy-map global_policy asa(config-pmap)# asa(config-pmap)# class class-default asa(config-pmap-c)# set connection decrement-ttl
The result:
asa# sh run . . . icmp unreachable rate-limit 10 burst-size 5 . . . policy-map global_policy class inspection_default inspect dns preset_dns_map inspect ftp . . . inspect icmp inspect sunrpc class class-default set connection decrement-ttl service-policy global_policy global . . .
Sources:
http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_tech_note09186a0080094e8a.shtml
http://packetu.com/content/view/50/