Cracking in the brickwork (or other masonry), especially in the mortar, is a sure sign of foundation problems. The foundation itself may be cracked or sinking. In any case, the foundation is no longer supporting the exterior masonry which tends to settle over the weak foundation area.
Cracking may be less evident on exterior surfaces such as wood frame. Here, look for bowing or gaps developing between joints.
Cracking of sheetrock or other interior wall surfaces may well indicate foundation damage. Sheetrock is rigid and will react to uneven pressure by cracking or gapping at the joints. Interior tile surfaces react much the same way as brickwork, cracking along the mortar. Wooden flooring may be more flexible and not show cracking, but may seem uneven and tilted.
Take notice if doors and/or windows begin to stick or will not close easily. The frames may be twisted out-of-square by uneven pressure of a shifting foundation.
If soil seems to be pulling away from the foundation, the foundation may be shifting or settling into a new and potentially damaging position. Periodically inspect where soil meets the foundation while gardening or performing routine house maintenance.