Question: Is there such a thing as an implied tie? Like some kind of symbol or notation that would specify to hold a note through the duration of all the notes on a pitch as if they were tied together. 

**Edit:** I am asking because I am wondering if there is a way to specify that instruments hold one tone (like a choir that is humming) instead of playing each note separately. The reason I am wondering is because I am using a notation program to write out some music, and then you can listen to it, and I want to hear it like a choir humming. I know about ties, but I just thought I'd check if there is such a thing in music.

**Edit:** By implied, I mean it isn't written in the music. In other words it is specified at the beginning of the part or something like that. 

**Edit:** I am using Noteworthy Composer.

Answer: 
As I understand your question, no there is not. A tie is always written out with a curved line connecting two or more notes of the same pitch. 

The only thing that I can think of that comes close is a dotted note. However, a dotted note is viewed as one note, not multiple notes tied together.
It depends on the instrument. The abbreviation "l.v." is used. It stands for "lasciare vibrare" in Italian, or "let vibrate" or as luser droog says, "let ring". It is used for percussion instruments like the tam-tam and timpani, and also for harp and similar instruments.

For piano music Beethoven uses "senza sordini" which means "without dampers", i.e. hold the damper pedal down. See the first movement of the Moonlight Sonata (Sonata number 14).

Your best bet is to just write instructions at the beginning telling the musician what to do.