The big limitation on magical powers in Mage comes from paradox driven by the counter-belief of non-mage observers. A little creative description can get around that issue; here’s some ideas to give characters reasons for concern given how coincidence leads to bigger and nastier magickal effects.
* The sound of far-off gunshots, soon repeated but much closer. (Stray shots can cause and justify a lot of damage.)
* The sound of squealing tires coming in the PCs direction. (Out of control car could hit them.)
* Loose bolts, blocks of broken concrete, and other debris found laying on sidewalks. (The buildings around them are unstable.)
* Groups of strangers breaking into violence. (Again, chance of getting caught in the crossfire.)
* An open fire hydrant spraying water over the street. (Slippery surface, also conduit for electricity if a live wire falls onto the wet street.)
* Rolling power blackouts throughout the city. (What cannot be seen does not violate the rules of Paradox.)
* Nearby cries of babies or people screaming for help. When investigated, nothing is found except trails of blood along the ground leading into clean solid walls. Witnesses in the area will claim to have neither seen nor heard anything unusual, and they have no idea where that blood came from. They seem frightened but won’t talk about it. (Sanity loss or Delirium-like affect forcing mundanes from acknowledging what they might have just seen.)
* Local street graffiti sprayed on walls and trains contains occult symbols or weird messages which mention the PCs by name. (Someone or something has targeted them, giving excuse to whatever horror lurks around the next corner.)