If one is truely hindu : 1. He understands the purpose of religion is to go inward and not make it a political force. 2. One understands truth has many sides to it, one should take up a path most best suited for himself and will have the common sense to understand that people are different and may chose differently. 3. One does not give centralizing powers which includes Political parties, pseudo religious organizations (RSS, VHP, monkeys (bajrang dals) to which will use you for their own dirty ends. 4. Atleast practices yama and niyama which include tolerance, expansiveness, inclusiveness, truth and above all ahimsa (which is much more than just nonviolence). 5. Does not confine himself to narrowness of cults such as christianity, islam, narrow castes and organized hinduism.
If one is truely secular then one is truely hindu.