What are some ways I can eliminate trash being littered in my community? I don't want to tackle this issue alone so the proposed ideas shouldn't be solo solutions I have to do by myself. FYI, I live in a condo community, within a suburban metropolitan region.
Trash littered within a community is unpleasant and can be hard to prevent if the culprits are unknown. Here are some ways to prevent trash from being littered in your community.

1) Engage the HOA
HOA groups often create and enforce policies for the residential communities they manage. Most likely, you are not the only resident observing the trash being littered around your neighborhood and there is a high chance that other neighbors share the discontent. If your townhouse community has an HOA, bringing this issue to their attention at the next HOA meeting may be a good way to start. With enough support from other residents and approval from the HOA board, guidelines can be set restricting any trash to be littered. HOA often also have the power, written into the contractual agreements signed by residents before move-in, to enforce rules they set. Penalties for residents refusing to comply with rules may range from thousands of dollars in fees to eviction. If new HOA rules making improper disposal of trash can be set, then residents will have to eventually comply, assuming the root cause is from within the community. HOAs may even help lead preventative strategies attempting to proactively address the problem. Some strategies include the installation of waste baskets for general use, increasing the frequency of waste management services, installing street signs, and/or employing third-party street cleaning services. 

2) Establish a Neighborhood Watch Group
A neighborhood watch, also called a crime watch is an organized group of civilians devoted to crime and vandalism prevention within a neighborhood, including littering. Similar to HOA organizations, members of watch groups are often intrinsically motivated to maintain a clean neighborhood and share the same common goals. Neighborhood watch groups can be as informal or formal as one would like, although informal methods may be easier to start if your community does not have such a group in place already. Typically, informal watch groups involve select community residents patrolling and monitoring the community looking out for any suspicious activity, crime, or other behavior breaking rules. A schedule is usually shared between volunteers listing out availabilities, procedures in case of emergencies, and contact information, including local law enforcement. Having an active neighborhood watch group monitoring the community will likely deter the culprits. Although the initial purpose of starting a watch group may be to catch and deter litterers, it is possible that the group also inadvertently encounters more serious and dangerous criminals who have gone unnoticed in the past. Depending on the danger of the threats, and if the watch group volunteers are inexperienced or untrained in handling more threatening situations, then risks can quickly escalate beyond what was anticipated. Therefore, the safety of the volunteers within the group is an important concern and should remain a high priority. 

3) Contact local law enforcement
Law enforcement will likely be able to assist in preventing trash to be littered in your community. Law enforcement is a public service and it can be argued that trash is impeding the well-being of the local public. A big advantage of involving law enforcement over creating a local neighborhood watch group is that the former has extensive experience and training in dealing with a wide range of threats, while the latter may not. For example, if the litterers also coincidentally happen to be wanted fugitives then law enforcement would be prepared to apprehend the criminals safely away from the community residents. Another advantage of involving law enforcement to eliminate trash being littered in your community is that they can adjust their levels of engagement depending on the severity of the issues. If the trash being littered is largely immaterial or non-threatening, then they may elect to install street signs warning culprits of the consequences of littering or occasionally patrol the street in marked police cars. Law enforcement may even leave a marked police car in plain sight within the community since the sight of a police car is known to reduce the chances of criminal activity in most cases. However, if trash being littered is significantly harming the residents (e.g., hazardous materials, food waste, heavy items, etc.), then law enforcement will likely elect to increase their engagement and may even dedicate an officer present at all times. As illustrated, some of the benefits of contacting law enforcement are the flexibility of engagement, the depth of their expertise, and nearly unlimited resources in combatting the littering issue.