I have heard of blood on the dance floor, but Blood on the Nishan Sahib?
The nishan sahib is the flag of the Sikh nation and Khalsa army. Every Gurdwara has one to show it's location. The Nishan sahib reminds us of all the shaheeds, and is a symbol of honour.
Views of people that agree with this practice:
Our shaheeds gave their blood for us, by doing this we show that we are ready to do the same.
If you haven't got the guts to just take a few drops of your blood to show respect for the shaheeds, how will you go to war for the panth.
Veiws of people that disagree with this practice:
Cutting yourself is self harming and is a mental disorder.
If you really want to show respect to the shaheeds, do seva for the panth and hopefully with Guru's kirpa, you too one day might become a shaheed.
Bravery is when you risk your life for humanity.
Conclusion:
Cutting yourself to clean the Nishan Sahib is just crazy and bizarre, if you really want to give your blood for the panth, fight for humanity and against injustices. Shaheed Baba Deep Singh Ji gave his blood for the Panth the real way.