cope
Bellingham's winters are often long and rainy, and it's the northernmost city of its size in the lower 48 states. If you visit between the months of October and May be prepared for a good deal of wind and precipitation.
crime
The crime rate is relatively low for an urban area by American standards. Violent crime perpetrated by strangers is nearly unheard of, but property crime is more common. If you are parked at a trailhead or in a park, keep your valuables out of sight, or better yet leave them where you're staying.
There are few areas of the city that couldn't be considered safe at all hours of the day and night. The downtown bar scene sometimes attracts a drunk and somewhat rowdy crowd at night, and a few street corners downtown attract groups of loiterers that have occasionally become belligerent. But overall no unusual precautions need be taken. Certain areas in Alabama neighbourhood should be avoided.
rail/trail crossings
When hiking in the area it's not unusual to have to cross the railroad tracks that hug the shoreline south of the city, or in some cases walk along the tracks though both are technically considered trespassing. Be sure to stay alert; while the numerous freight trains that pass through make plenty of noise, the passenger trains are surprisingly quiet and can easily sneak up on an unwary hiker.