Broken heart – rejects or ends romance
Checkmark – accepts the offer
Clenched fist – aggressive response
Crossed swords – initiates combat
Diamond – Charming response
Gavel/hammer – direct, blunt response
Halo over wings – helpful/kind
Head silhouette – calls on companion to allow them to respond
Heart – flirty response
Laughing facemask – Joker, humorous response
Olive Branch/leafy branch – Diplomatic response
X – Rejects the offer
Rarer Icons:
Falling Coins – Bribe, pay, or extort response.
Fingers crossed – Lie
Questionmark – Investigate, ask questions to learn more about something
Star Unique choice with unusual or special outcome
Here's a few links further describing them:
http://img29.imageshack.us/img29/6516/iconguide.jpg
http://img215.imageshack.us/img215/359/iconguide2.jpg
Hope that helps you out !!