I know you mean well, so I will answer your question. When a christian recieves the Holy Spirit, the Spirit writes the Father's commandments on his heart and mind.
Jeremiah 31:33
"This is the covenant I will make with the people of Israel after that time," declares the LORD. "I will put my law in their minds and write it on their hearts. I will be their God, and they will be my people.
^ This same prophecy is repeated in Hebrews 10:16.
If you have an inner desire to obey God's commandments, you can be sure that Spirit is dwelling in your mind, and that you're growing in His ways. But if you dislike obeying God's commandments, and try to come up with irrational excuses for disobeying them, like most people do, this is what the scriptures say about you:
Romans 8:7
The mind governed by the flesh is hostile to God; it does not submit to God's law, nor can it do so.
So, to answer your original question, the mark of a true christian is his love for God. And His love for God is manifested in this way:
1 John 5:3
In fact, this is love for God: to keep his commands. And his commanments are not burdensome.