The easiest association is with sacrifice and fasting. That's what we're doing on this Ash Wednesday, after all. But I'd suggest that the very scriptures we read tell us that, if we use it in this manner, we are being hypocritical: seeking to wear the outward sign of humility while proclaiming to everyone that we are the most humble of all.
I think that the point of that ashen cross isn't to proclaim that we are so humble/sacrificial. It's to remind us and everyone that sees it that we are dust and unto dust we shall return. All shall die and all must rely on the mercy of God. That's the real point of the Lenten journey after all. It's not an escapade into self discovery. It's an escapade into discovering God's mercy.