What is the special die with pictograms in Monopoly used for?
It appears you have the Championship Edition (or the Mega Edition or some other recent modified version), which includes a "speed die" (that third die) for speeding up the game, though it's definitely not part of the original game. There are two "bus" faces, and one "Mr. Monopoly" face.

I found these rules on Hasbro's site explaining how it works. The PDF was was reluctant to load for me, so I've quoted them here:


  
  When starting the game, hand out an extra $1,000 to each player 
  (two $500s should work). The game moves fast and you'll need 
  the extra cash to buy and build. 
  Do not use the Speed Die until you've landed on or passed over GO for the first time. Once you collect that first $200 salary, you'll use the Speed Die for the rest of the game. This means that some players will start using the die before others. 
  Once you start using the Speed Die, roll it along with the two 
  white dice on your turn. Then do the following depending on 
  what you rolled.
  
  
  1, 2, or 3: Add this number to the roll of the two white dice. You'll zoom around the board. 
  Bus: This lets you "get off the bus early." Look at the two white dice. You can move the value of one die, the other die, or the sum of both dice. So if you rolled a 1 and a 5, you can move 1 space, 5 spaces, or 6 spaces: it's your choice.
  Mr. Monopoly: First, move the sum of the two white dice 
  and resolve the space you land on (such as drawing a card, 
  buying the property, paying rent, etc.). Then, one of two 
  things will happen depending on whether or not there is still 
  property in the bank. 
  
  YES, there is property in the bank -- Advance to the NEXT 
  property that the bank still holds and buy it if you wish. If you 
  don't want to buy this property, move to the space anyway 
  and put the property up for auction. 
  
  NO, there are no more properties in the bank -- Advance to the 
  NEXT property on which you will owe another player money. 
  
  
  
  A few minor details: 
  
  
  Only the white dice are used when determining if you rolled doubles. Do not look at the Speed Die. 
  If you roll a three-of-a-kind (all of the dice show the same number), 
  you can move anywhere you want on the board!
  If you get sent to jail during your move (either by landing on the "Go 
  to Jail" space or by rolling doubles three times in a row) then your turn 
  is over and you do not get to use the Speed Die for that turn. 
  Use the white dice ONLY when rolling to get out of jail.
  Use the sum of all three dice when determining how much to pay on a utility. Note: The Bus and Mr. Monopoly are valued at 0.