To write 'Maulwi saheb' (or similar appellations) for yourself without a valid Islamic excuse is sinful and against the ruling of the Qur'ān. 

Allah says: 

"He knows you very well – since He has created you from clay, and when you were foetuses in your mothers’ wombs; therefore do not, on your own, claim yourselves to be clean; He well knows who are the pious." [Qur'ān 53:32] 

Allah further says:

"Did you not see those who proclaim their piety? In fact Allah purifies whomever He wills." [Qur'ān 4:49]

It is stated in the Hadīth that the Messenger of Allah said:

من قال انا عالم فهـو جاهـل  

"Whosoever says; I am a scholar [ālim] is ignoramus [jāhil]." [Narrated by Tabarāni in al-Awsat with a sound chain from Abdullah Ibn Umr]  

However, if an individual is truly a scholar, but the masses are unaware of his virtues, then, only with that pure intention of making the masses aware so that they may seek blessings and guidance, there is no problem with him showing his knowledge. Like Yusuf (Alaihis-Salām) said, "انّى حفيظ عليم" (Verily I am the protector and knower). However, this is only for those who are truly scholars. 

To believe yourself to be better than someone else is Arrogance [Takabbur], for such a person this verse is sufficient; Allah says:

"Is there not in Hell a residence for the arrogant?" 

[Qur'ān 39:60] 

[Fatāwā Ridawiyyah, volume 23, pages 726, 727 & 650]

Translated by Muhammad Kalim (Preston)