There will be tour guides wandering the parque, but they will ask for money to take you up to the cross. The tourismo police escort tourists for free 10am/3pm each day. Or better yet, walk up there yourself. From the park, head up north on 4a ave norte, until you hit the end, make a right turn, for couple blocks, you'll see a nice residential area on your left, follow the gradual uphill walk, then you'll see an intersection, on your left is the way to the hill (signs). Follow the steep steps/walk the motor roads (i like the vehicle roads because it's less prone to mugging). During day time, I feel very safe walking there alone, with a flow of traffic, and very visual presence of police everywhere. It's an amazing sights to see Antigua and Volcan Aqua.
In general, Antigua Guatemala is much safer than the rest of Guatemala. There is tourist police patrolling in the town. You can usually walk in the town at night without any problems. However, don't go to Cerro de la Cruz alone. You'd better go with the tourist police that escorts tourists to the hill twice a day (10:00am in the morning and 3:00pm in the afternoon) free of charge. The tourist police can be found on 4a Ave at the northeast of the Central Park.
A danger spot to mention is the cross on a hill overlooking Antigua. Crosses are customarily erected on a highpoint above Latin cities. If you choose to visit such shrines, do so in the morning. Robbery and assault are greater and greater possibilities as the day wears on.
If you are planning to walk the ten minutes up the hill to Cerro de Cruz to take in the panaroma, register with the tourist police beforehand so you can be accompanied. There have been many reports of theft and should not be done independently.
The fascinating view offered by the cerrito is magnificent. Although there are armed guards it is not advisable to climb venture out in the hillside alone or at night.
nice view from cross walk ,under the armed guardians protection...agression...and crimes against tourists (one of them 15th of november 1996)