There is nothing wrong with trimming the moustache or shave it altogether
Question

                I trim my moustache so short that it cant be seen... is that correct? Are we allowed to say Al Hussayn was a Martyr?.
Praise be to Allah.The scholars are 
    unanimously agreed that it is permissible to trim or cut the moustache, 
    because of the many ahaadeeth that have been narrated concerning that, such 
    as the words of the Prophet  (peace and blessings of Allaah be upon 
    him): “Let the beard grow, and trim the moustache.” Narrated by al-Bukhaari 
    (5442). And he  (peace and blessings of Allaah be upon him) said: 
    “Whoever does not remove anything from the moustache is not one of us.” 
    Narrated by al-Tirmidhi (2685) and classed as saheeh by al-Albaani in 
    Saheeh al-Tirmidhi. 
Al-Nawawi (may Allaah have 
    mercy on him) said in al-Majmoo’ (1/340)” As for cutting the 
    moustache, there is unanimous agreement that it is Sunnah. End quote. 
But there is a difference 
    of opinion among the scholars as to how much may be removed. 
Al-Shawkaani said in 
    Nayl al-Awtaar (1/148): The people differed as to the amount that may be 
    cut from the moustache. Many of the salaf were of the view that it may be 
    removed completely and shaved off, because of the apparent meaning of the 
    words shave and remove completely. This was the view of the Kufis [and is 
    one view narrated from Imam Ahmad. What is meant by the Kufis is the 
    followers of Abu Haneefah (may Allaah have mercy on him)]. 
Many others were of the 
    view that it is not allowed to shave it or remove it completely. This was 
    the view of Maalik [and of al-Shaafa’i and of Ahmad, according to another 
    report from him]. 
Imam Maalik was very strict 
    about shaving the moustache and regarded it as mutilation for which a person 
    deserved to be disciplined. He said that shaving it was a bid’ah 
    (innovation) which had appeared among the people. This was narrated from him 
    by al-Nawawi in al-Majmoo’ and by Ibn al-Qayyim in Zaad al-Ma’aad 
    and others, but the majority of scholars were of a different view, as they 
    thought that there was nothing wrong with shaving or cutting it, although 
    they differed as to which is better. End quote. 
Al-Mardaawi said in 
    al-Insaaf (1/121): He may shave his moustache or trim the ends, but 
    shaving is better. This was stated by him [i.e., Imam Ahmad]. End quote.  
Ibn al-Qayyim stated in 
    Zaad al-Ma’aad (1/171) that Imam Ahmad (may Allaah have mercy on him) 
    said: If he shaves it there is nothing wrong with it, and if he cuts it 
    there is nothing wrong with it. The evidence that Imam Ahmad quoted for that 
    is that the ahaadeeth enjoined shaving and cutting. 
Hence the brother who asked 
    this question may know that there is nothing wrong with what he is doing, 
    although it is better to cut the moustache so that the edge of the lip 
    appears, and not to remove it altogether, because this is what the Messenger 
     (peace and blessings of Allaah be upon him) used to do. It was narrated 
    that Ibn ‘Abbaas (may Allaah be pleased with him) said: The Prophet  
    (peace and blessings of Allaah be upon him) used to cut his moustache. Narrated by Ahmad (2733). Shaykh Ahmad Shaakir said: Its isnaad is saheeh.