The weapons you find will always indicate what you will fight up ahead:
WHAT IS AHEAD
This does not means anything, as they are found throughout the game.
Indicates that a platoon of enemy soldiers is close by.
This indicates that long distance firing will be needed soon, or heavy armor is close by.
Indicates possible snipers or heavy armor.
One pistol indicates Paranormal activity is nearby. Two pistols do not mean anything.
Indicates that lots of enemy soldiers, mechs, etc. are near. Basically, there is a lot of everything coming up. It also indicates that the end of the game is near when more quantities of them are found.
Indicates that a Mech, Leviathan, or heavy armor is close by (not so much Heavy armor).
This does not usually mean anything, as they are found throughout the game. However, it may indicate heavy armor.
This indicates that there will be lots of any type of soldiers nearby.